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  19. </a></div> <!----></nav>  <ul class="sidebar-links"><li><section class="sidebar-group depth-0"><p class="sidebar-heading open"><span>Rust入门教程（九）：实战演练：一个简单的 grep 程序</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#一、接收命令行参数" class="sidebar-link">一、接收命令行参数</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#二、读取文件" class="sidebar-link">二、读取文件</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#三、重构-改进模块和错误处理" class="sidebar-link">三、重构：改进模块和错误处理</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#_3-1-四个问题提炼" class="sidebar-link">3.1 四个问题提炼</a></li><li class="sidebar-sub-header"><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#_3-2-二进制程序关注点分离的指导性原则" class="sidebar-link">3.2 二进制程序关注点分离的指导性原则</a></li></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#四、使用-tdd-测试驱动开发-开发库功能" class="sidebar-link">四、使用 TDD（测试驱动开发）开发库功能</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#五、使用环境变量" class="sidebar-link">五、使用环境变量</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#六、将错误消息写进标准错误而不是标准输出" class="sidebar-link">六、将错误消息写进标准错误而不是标准输出</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#七、完整代码" class="sidebar-link">七、完整代码</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#八、案例-代码统计" class="sidebar-link">八、案例：代码统计</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#_8-1-基本功能介绍" class="sidebar-link">8.1 基本功能介绍</a></li><li class="sidebar-sub-header"><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#_8-2-可拓展功能" class="sidebar-link">8.2 可拓展功能</a></li><li class="sidebar-sub-header"><a href="/rust_camp_tutorial/Rust%E6%96%87%E6%A1%A3/Rust%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B%EF%BC%88%E4%B9%9D%EF%BC%89.html#_8-3-代码仓库及说明" class="sidebar-link">8.3 代码仓库及说明</a></li></ul></li></ul></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="rust入门教程-九-实战演练-一个简单的-grep-程序"><a href="#rust入门教程-九-实战演练-一个简单的-grep-程序" class="header-anchor">#</a> Rust入门教程（九）：实战演练：一个简单的 grep 程序</h1> <blockquote><p>本章将介绍 Rust 在实际开发中的使用，并用官方文档上的项目（一个简单版本的 grep 命令）展开讲解，最后将利用之前所学，自己实现一个代码统计的 Rust 小项目。
    20. 

  20. 要实现的 grep 命令功能很简单，就是在指定文件中查找指定文字。grep 命令接收一个文件名和字符串作为输入参数，然后读取文件内容，搜索包含指定字符串的行，最终将这些匹配的行打印输出。</p></blockquote> <p>下面开始实战演示。</p> <h2 id="一、接收命令行参数"><a href="#一、接收命令行参数" class="header-anchor">#</a> 一、接收命令行参数</h2> <p>我们预计使用如下命令来执行该程序：</p> <div class="language-bash extra-class"><pre class="language-bash"><code><span class="token function">cargo</span> run <span class="token operator">&lt;</span>string<span class="token operator">&gt;</span> <span class="token operator">&lt;</span>filename<span class="token operator">&gt;</span>
    21. 

  21. </code></pre></div><p>因此我们首先要读取命令行中的参数，我们导入函数 <code>use std::env::args()</code>，<code>args()</code> 函数返回一个迭代器，迭代器部分的内容将在后面才会介绍。然后使用 <code>collect</code> 方法，将迭代器中的值转化成一个集合，但是该函数不能处理命令行中非 <code>Unicode</code> 的字符（这种情况可以使用 <code>env::args _os()</code> 函数，这种情况下返回的迭代器值的类型是 <code>OsString</code>，在这里不做介绍）。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    22. 

  22. 

  23. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    24. 

  24.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    25. 

  25.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    26. 

  26.     <span class="token keyword">let</span> filename <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    27. 

  27.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;{:?}&quot;</span><span class="token punctuation">,</span> args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    28. 

  28.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;Search String {}&quot;</span><span class="token punctuation">,</span> search_string<span class="token punctuation">)</span><span class="token punctuation">;</span>
    29. 

  29.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;In file {}&quot;</span><span class="token punctuation">,</span> filename<span class="token punctuation">)</span><span class="token punctuation">;</span>
    30. 

  30. <span class="token punctuation">}</span>
    31. 

  31. </code></pre></div><div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ cargo run string filename
    32. 

  32.    <span class="token class-name">Compiling</span> minigrep v0<span class="token number">.1</span><span class="token punctuation">.</span><span class="token number">0</span> <span class="token punctuation">(</span><span class="token operator">/</span>home<span class="token operator">/</span>cherry<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep<span class="token punctuation">)</span>
    33. 

  33.     <span class="token class-name">Finished</span> dev <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>29s
    34. 

  34.      <span class="token class-name">Running</span> `target<span class="token operator">/</span>debug<span class="token operator">/</span>minigrep string filename`
    35. 

  35. <span class="token punctuation">[</span><span class="token string">&quot;target/debug/minigrep&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;string&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;filename&quot;</span><span class="token punctuation">]</span>
    36. 

  36. <span class="token class-name">Search</span> <span class="token class-name">String</span> string
    37. 

  37. <span class="token class-name">In</span> file filename
    38. 

  38. </code></pre></div><p>根据程序执行结果我们能够得知：返回的第一个参数永远都是该程序的二进制文件（对应 <code>args[0]</code>），从第二个参数开始才是从命令行输入的各种参数（对应 <code>args[1]</code> ...）。</p> <h2 id="二、读取文件"><a href="#二、读取文件" class="header-anchor">#</a> 二、读取文件</h2> <p>首先导入模块 <code>use std::fs</code>，用于处理和文件相关的事务，<code>read_to_string()</code> 用来读取文件中的内容，将其转化成字符串。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    39. 

  39. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    40. 

  40. 

  41. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    42. 

  42.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    43. 

  43.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    44. 

  44.     <span class="token keyword">let</span> filename <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    45. 

  45.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;{:?}&quot;</span><span class="token punctuation">,</span> args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    46. 

  46.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;Search String {}&quot;</span><span class="token punctuation">,</span> search_string<span class="token punctuation">)</span><span class="token punctuation">;</span>
    47. 

  47.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;In file {}&quot;</span><span class="token punctuation">,</span> filename<span class="token punctuation">)</span><span class="token punctuation">;</span>
    48. 

  48. 

  49.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>filename<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">expect</span><span class="token punctuation">(</span><span class="token string">&quot;该文件不存在&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    50. 

  50.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    51. 

  51. <span class="token punctuation">}</span>
    52. 

  52. </code></pre></div><p>输出结果为：</p> <div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ cargo run string poem    
    53. 

  53.     <span class="token class-name">Finished</span> dev <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    54. 

  54.      <span class="token class-name">Running</span> `target<span class="token operator">/</span>debug<span class="token operator">/</span>minigrep string poem`
    55. 

  55. <span class="token punctuation">[</span><span class="token string">&quot;target/debug/minigrep&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;string&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;poem&quot;</span><span class="token punctuation">]</span>
    56. 

  56. <span class="token class-name">Search</span> <span class="token class-name">String</span> string
    57. 

  57. <span class="token class-name">In</span> file poem
    58. 

  58. 文件内容<span class="token punctuation">:</span>
    59. 

  59. <span class="token class-name">Hold</span> fast to dreams
    60. 

  60. <span class="token class-name">For</span> <span class="token keyword">if</span> dreams die
    61. 

  61. <span class="token class-name">Life</span> is a broken<span class="token operator">-</span>winged bird
    62. 

  62. <span class="token class-name">That</span> can never fly
    63. 

  63. <span class="token class-name">Hold</span> fast to dreams
    64. 

  64. <span class="token class-name">For</span> when dreams go
    65. 

  65. <span class="token class-name">Life</span> is a barren field
    66. 

  66. <span class="token class-name">Frozen</span> only with snow
    67. 

  67. 

  68. <span class="token class-name">To</span> see a world <span class="token keyword">in</span> a grain of sand<span class="token punctuation">,</span>
    69. 

  69. <span class="token class-name">And</span> a heaven <span class="token keyword">in</span> a wild flower<span class="token punctuation">,</span>
    70. 

  70. <span class="token class-name">Hold</span> infinity <span class="token keyword">in</span> the palm of your hand<span class="token punctuation">,</span>
    71. 

  71. <span class="token class-name">And</span> eternity <span class="token keyword">in</span> an hour<span class="token punctuation">.</span>
    72. 

  72. </code></pre></div><p>当然目前看来所有逻辑都放在了主函数中，并且很多错误情况都没有考虑。一般情况下一个函数只做一件事，如果代码逐渐变多，代码维护将变得越来越困难。代码越少重构越简单，因此下一节将对代码进行重构。</p> <h2 id="三、重构-改进模块和错误处理"><a href="#三、重构-改进模块和错误处理" class="header-anchor">#</a> 三、重构：改进模块和错误处理</h2> <h3 id="_3-1-四个问题提炼"><a href="#_3-1-四个问题提炼" class="header-anchor">#</a> 3.1 四个问题提炼</h3> <p>我们仔细观察一下目前的代码，主要有四个方面的问题。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    73. 

  73. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    74. 

  74. 

  75. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    76. 

  76.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    77. 

  77.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    78. 

  78.     <span class="token keyword">let</span> filename <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    79. 

  79.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;{:?}&quot;</span><span class="token punctuation">,</span> args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    80. 

  80.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;Search String {}&quot;</span><span class="token punctuation">,</span> search_string<span class="token punctuation">)</span><span class="token punctuation">;</span>
    81. 

  81.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;In file {}&quot;</span><span class="token punctuation">,</span> filename<span class="token punctuation">)</span><span class="token punctuation">;</span>
    82. 

  82. 

  83.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>filename<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">expect</span><span class="token punctuation">(</span><span class="token string">&quot;该文件不存在&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    84. 

  84.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    85. 

  85. <span class="token punctuation">}</span>
    86. 

  86. </code></pre></div><ol><li>主函数负责的功能较多，既要负责命令行参数解析，又要负责读取文件。而程序编写的原则就是一个函数负责一个功能，因此要将主函数拆分；</li> <li><code>search_string</code>、<code>filename</code> 和 <code>content</code> 变量，在程序越来越大之后，变量也会越来越多，将难以追踪每一个变量的实际意义。解决办法是将这些变量放入一个结构体中，从而使其用途更加清晰；</li> <li>读取文件时，使用 <code>expect</code> 处理错误，但未对其读取错误的原因进行细分，因为文件打不开可能是文件不存在，文件权限不够，文件损坏等原因；</li> <li>对于命令行参数的错误处理，若输入的参数没有两个，那么程序本身就会报错，并且能够预料到的错误一定是 <code>Out of bound</code> 这类的错误，但是对于使用者来说，可能并不清楚这个所谓的 <strong>越界错误</strong> 意味着什么，无法清晰解释错误的具体原因。因此最好要将所有错误处理集中到一起，将来开发者要考虑错误处理的时候，就只要处理这一处代码，这样也能保证为用户打印出有意义的错误信息，而不是只有程序员能看懂的 <code>Out of bound</code>。</li></ol> <h3 id="_3-2-二进制程序关注点分离的指导性原则"><a href="#_3-2-二进制程序关注点分离的指导性原则" class="header-anchor">#</a> 3.2 二进制程序关注点分离的指导性原则</h3> <ul><li>将程序拆分为 <code>main.rs</code> 和 <code>lib.rs</code>，将业务逻辑放入 <code>lib.rs</code></li> <li>当命令行解析逻辑较少时，将它放在 <code>main.rs</code> 也行</li> <li>当命令行解析逻辑变复杂时，需要将它从 <code>main.rs</code> 提取到 <code>lib.rs</code></li></ul> <p>经过上述拆分，留在 <code>main</code> 的功能有：</p> <ul><li>使用参数值调用命令行解析逻辑</li> <li>进行其它配置</li> <li>调用 <code>lib.rs</code> 中的 <code>run</code> 函数</li> <li>处理 <code>run</code> 函数可能出现的错误</li></ul> <p>因此放在 <code>main.rs</code> 中的代码量应足够小，小到直接阅读代码就可以确保代码的正确性。将业务逻辑放入 <code>lib.rs</code> 中也方便进行功能测试。</p> <p>针对上面说的四个方面的问题，我们逐一进行解决。</p> <p><strong>1. 拆分出命令行参数提取功能</strong></p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    87. 

  87. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    88. 

  88. 

  89. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    90. 

  90.     <span class="token punctuation">...</span> 
    91. 

  91.     <span class="token keyword">let</span> <span class="token punctuation">(</span>search_string<span class="token punctuation">,</span> filename<span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token function">parse_config</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    92. 

  92.     <span class="token punctuation">...</span>
    93. 

  93. <span class="token punctuation">}</span>
    94. 

  94. <span class="token keyword">fn</span> <span class="token function-definition function">parse_config</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token punctuation">(</span><span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token punctuation">,</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    95. 

  95.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    96. 

  96.     <span class="token keyword">let</span> filename <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    97. 

  97.     <span class="token punctuation">(</span>search_string<span class="token punctuation">,</span> filename<span class="token punctuation">)</span>
    98. 

  98. <span class="token punctuation">}</span>
    99. 

  99. </code></pre></div><p>我们发现，<code>parse_config</code> 函数目前返回一个元组，但是在主函数中，又将该元组拆分出来，赋值给两个变量，这样感觉有点“脱裤子放屁”的感觉，来回折腾。实际上这种情况就说明程序中这样设计数据结构是不正确的。因此较好的做法就是将返回的元组中的变量放入一个结构体。</p> <p><strong>2. 创建结构体</strong></p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">struct</span> <span class="token type-definition class-name">Config</span> <span class="token punctuation">{</span>
    100. 

  100.     search_string<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    101. 

  101.     filename<span class="token punctuation">:</span> <span class="token class-name">String</span>
    102. 

  102. <span class="token punctuation">}</span>
    103. 

  103. 

  104. <span class="token keyword">fn</span> <span class="token function-definition function">parse_config</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    105. 

  105.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    106. 

  106.     <span class="token keyword">let</span> filename <span class="token operator">=</span> <span class="token operator">&amp;</span>args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    107. 

  107.     <span class="token class-name">Config</span> <span class="token punctuation">{</span> search_string<span class="token punctuation">,</span> filename <span class="token punctuation">}</span>
    108. 

  108. <span class="token punctuation">}</span>
    109. 

  109. </code></pre></div><p>这里我们创建一个叫 <code>Config</code> 的结构体，将 <code>search_string</code> 和 <code>filename</code> 两个变量放入结构体。但是上面的代码会报错，这是因为在函数 <code>parse_config</code> 中，<code>args</code> 参数是切片类型，是没有所有权的（它的所有权被 <code>main</code> 函数拥有），而在最后要返回一个 <code>Config</code> 结构体对象，该结构体需要占用所有权，因此会报错。</p> <p>这里用一个简单的方法来处理，就是创建 <code>args[1]</code> 和 <code>args[2]</code> 的两个副本，尽管这样会损失性能。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">fn</span> <span class="token function-definition function">parse_config</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    110. 

  110.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    111. 

  111.     <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    112. 

  112.     <span class="token class-name">Config</span> <span class="token punctuation">{</span> search_string<span class="token punctuation">,</span> filename <span class="token punctuation">}</span>
    113. 

  113. <span class="token punctuation">}</span>
    114. 

  114. </code></pre></div><p>我们再来看 <code>parse_config</code> 函数，它返回的是一个结构体，实际上是要创建一个新的结构体，因此我们最好再实现该结构体的 <code>new</code> 函数。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">impl</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    115. 

  115.     <span class="token keyword">fn</span> <span class="token function-definition function">new</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    116. 

  116.         <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    117. 

  117.         <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    118. 

  118.         <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    119. 

  119.             search_string<span class="token punctuation">,</span>
    120. 

  120.             filename<span class="token punctuation">,</span>
    121. 

  121.         <span class="token punctuation">}</span>
    122. 

  122.     <span class="token punctuation">}</span>
    123. 

  123. <span class="token punctuation">}</span>
    124. 

  124. </code></pre></div><p>这里就是将刚刚的 <code>parse_config</code> 变成了结构体 <code>Config</code> 的函数。重构后的完整代码如下：</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    125. 

  125. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    126. 

  126. 

  127. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    128. 

  128.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    129. 

  129.     <span class="token keyword">let</span> config <span class="token operator">=</span> <span class="token class-name">Config</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    130. 

  130.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">expect</span><span class="token punctuation">(</span><span class="token string">&quot;该文件不存在&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    131. 

  131.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    132. 

  132. <span class="token punctuation">}</span>
    133. 

  133. 

  134. <span class="token keyword">struct</span> <span class="token type-definition class-name">Config</span> <span class="token punctuation">{</span>
    135. 

  135.     search_string<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    136. 

  136.     filename<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    137. 

  137. <span class="token punctuation">}</span>
    138. 

  138. 

  139. <span class="token keyword">impl</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    140. 

  140.     <span class="token keyword">fn</span> <span class="token function-definition function">new</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    141. 

  141.         <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    142. 

  142.         <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    143. 

  143.         <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    144. 

  144.             search_string<span class="token punctuation">,</span>
    145. 

  145.             filename<span class="token punctuation">,</span>
    146. 

  146.         <span class="token punctuation">}</span>
    147. 

  147.     <span class="token punctuation">}</span>
    148. 

  148. <span class="token punctuation">}</span>
    149. 

  149. </code></pre></div><p><strong>3. 错误处理</strong></p> <p>我们不输入参数进行运行，不出预料的会产生下面的错误：</p> <div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ cargo run       
    150. 

  150. warning<span class="token punctuation">:</span> field is never read<span class="token punctuation">:</span> `search_string`
    151. 

  151.   <span class="token operator">-</span><span class="token punctuation">-&gt;</span> src<span class="token operator">/</span>main<span class="token punctuation">.</span>rs<span class="token punctuation">:</span><span class="token number">19</span><span class="token punctuation">:</span><span class="token number">5</span>
    152. 

  152.    <span class="token operator">|</span>
    153. 

  153. <span class="token number">19</span> <span class="token operator">|</span>     search_string<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    154. 

  154.    <span class="token closure-params"><span class="token closure-punctuation punctuation">|</span>     <span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span><span class="token operator">^</span>
    155. 

  155.    <span class="token closure-punctuation punctuation">|</span></span>
    156. 

  156.    <span class="token operator">=</span> note<span class="token punctuation">:</span> `<span class="token attribute attr-name">#[warn(dead_code)]</span>` on by default
    157. 

  157. 

  158. warning<span class="token punctuation">:</span> `minigrep` <span class="token punctuation">(</span>bin <span class="token string">&quot;minigrep&quot;</span><span class="token punctuation">)</span> generated <span class="token number">1</span> warning
    159. 

  159.     <span class="token class-name">Finished</span> dev <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    160. 

  160.      <span class="token class-name">Running</span> `target<span class="token operator">/</span>debug<span class="token operator">/</span>minigrep`
    161. 

  161. thread <span class="token lifetime-annotation symbol">'main</span>' panicked at <span class="token lifetime-annotation symbol">'index</span> out of bounds<span class="token punctuation">:</span> the len is <span class="token number">1</span> but the index is <span class="token number">1</span>'<span class="token punctuation">,</span> src<span class="token operator">/</span>main<span class="token punctuation">.</span>rs<span class="token punctuation">:</span><span class="token number">25</span><span class="token punctuation">:</span><span class="token number">29</span>
    162. 

  162. note<span class="token punctuation">:</span> run with `<span class="token constant">RUST_BACKTRACE</span><span class="token operator">=</span><span class="token number">1</span>` environment variable to display a backtrace
    163. 

  163. </code></pre></div><p>即 <strong>越界错误</strong>，这对于用户来说是无法理解的，我们当然可以在 <code>new</code> 函数中添加这样的判断语句，</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">if</span> args<span class="token punctuation">.</span><span class="token function">len</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">3</span> <span class="token punctuation">{</span>
    164. 

  164.     <span class="token macro property">panic!</span><span class="token punctuation">(</span><span class="token string">&quot;输入参数错误，请输入两个参数。&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    165. 

  165. <span class="token punctuation">}</span>
    166. 

  166. </code></pre></div><p>但是这样仍然会有编译器的其他信息，一般情况下，使用 <code>panic</code> 通常是程序本身的问题，但是像这类输入参数少的问题属于程序使用的问题，因此我们还需要进行改进，可以返回 <code>Result</code> 枚举，代码如下。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    167. 

  167. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    168. 

  168. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>process<span class="token punctuation">;</span>
    169. 

  169. 

  170. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    171. 

  171.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    172. 

  172.     <span class="token keyword">let</span> config <span class="token operator">=</span> <span class="token class-name">Config</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">unwrap_or_else</span><span class="token punctuation">(</span><span class="token closure-params"><span class="token closure-punctuation punctuation">|</span>err<span class="token closure-punctuation punctuation">|</span></span> <span class="token punctuation">{</span>
    173. 

  173.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;参数解析错误：{}&quot;</span><span class="token punctuation">,</span> err<span class="token punctuation">)</span><span class="token punctuation">;</span>
    174. 

  174.         <span class="token namespace">process<span class="token punctuation">::</span></span><span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    175. 

  175.     <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    176. 

  176.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">expect</span><span class="token punctuation">(</span><span class="token string">&quot;该文件不存在&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    177. 

  177.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    178. 

  178. <span class="token punctuation">}</span>
    179. 

  179. 

  180. <span class="token keyword">struct</span> <span class="token type-definition class-name">Config</span> <span class="token punctuation">{</span>
    181. 

  181.     search_string<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    182. 

  182.     filename<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    183. 

  183. <span class="token punctuation">}</span>
    184. 

  184. 

  185. <span class="token keyword">impl</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    186. 

  186.     <span class="token keyword">fn</span> <span class="token function-definition function">new</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token class-name">Config</span><span class="token punctuation">,</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    187. 

  187.         <span class="token keyword">if</span> args<span class="token punctuation">.</span><span class="token function">len</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">3</span> <span class="token punctuation">{</span>
    188. 

  188.             <span class="token keyword">return</span> <span class="token class-name">Err</span><span class="token punctuation">(</span><span class="token string">&quot;输入参数个数不足，请输入两个参数。&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    189. 

  189.         <span class="token punctuation">}</span>
    190. 

  190.         <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    191. 

  191.         <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    192. 

  192.         <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token class-name">Config</span> <span class="token punctuation">{</span>
    193. 

  193.             search_string<span class="token punctuation">,</span>
    194. 

  194.             filename<span class="token punctuation">,</span>
    195. 

  195.         <span class="token punctuation">}</span><span class="token punctuation">)</span>
    196. 

  196.     <span class="token punctuation">}</span>
    197. 

  197. <span class="token punctuation">}</span>
    198. 

  198. </code></pre></div><p>如果参数个数超过 2 个，则返回 <code>Err</code> 的变体，否则返回 <code>Ok</code>。主函数中，<code>unwrap_or_else</code> 函数的含义是，如果枚举返回的是 <code>Ok</code>，那么就取出 <code>Ok</code> 变体中的值返回，若枚举返回的是 <code>Err</code>，那么就调用一个闭包（匿名函数，闭包具体内容将来会介绍），然后使用 <code>process::exit(1)</code> 将程序返回，这样就不会有编译器的其他信息了。</p> <div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ cargo run
    199. 

  199.    <span class="token class-name">Compiling</span> minigrep v0<span class="token number">.1</span><span class="token punctuation">.</span><span class="token number">0</span> <span class="token punctuation">(</span><span class="token operator">/</span>home<span class="token operator">/</span>cherry<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep<span class="token punctuation">)</span>
    200. 

  200.     <span class="token class-name">Finished</span> dev <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>33s
    201. 

  201.      <span class="token class-name">Running</span> `target<span class="token operator">/</span>debug<span class="token operator">/</span>minigrep`
    202. 

  202. 参数解析错误：输入参数个数不足，请输入两个参数。
    203. 

  203. </code></pre></div><p><strong>4. 功能模块化</strong></p> <p>一个函数只处理一个功能，因此我们将业务逻辑（即读取文件内容）功能提取到一个新的函数中。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">fn</span> <span class="token function-definition function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">:</span> <span class="token class-name">Config</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    204. 

  204.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">expect</span><span class="token punctuation">(</span><span class="token string">&quot;该文件不存在&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    205. 

  205.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    206. 

  206. <span class="token punctuation">}</span>
    207. 

  207. </code></pre></div><p>然后我们进行 <code>run</code> 函数的错误处理。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">fn</span> <span class="token function-definition function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">:</span> <span class="token class-name">Config</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token class-name">Box</span><span class="token operator">&lt;</span><span class="token keyword">dyn</span> <span class="token class-name">Error</span><span class="token operator">&gt;&gt;</span> <span class="token punctuation">{</span>
    208. 

  208.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token operator">?</span><span class="token punctuation">;</span>
    209. 

  209.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    210. 

  210.     <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    211. 

  211. <span class="token punctuation">}</span>
    212. 

  212. </code></pre></div><p>这里 <code>result&lt;(), Box&lt;dyn Error&gt;&gt;</code> 中第一个参数是空，第二个参数只要理解是一个实现了 <code>Error</code> 这个 <code>trait</code> 的类型，这样函数便可以在不同场景下返回不同的错误类型。</p> <p>因为 <code>expect</code> 会引起恐慌，因此将其去掉，改成 <code>?</code>，<code>?</code> 运算符遇到错误不会恐慌，它会将错误值返回给函数的调用者，如果没有发生错误，那么我们最后返回一个 <code>Ok()</code>。</p> <p>这时编译器会在 <code>run(config)</code> 出给予警告：<code>this 'Result' may be an 'Err' variant, which should be handled</code>，这说明函数返回值是一个 <code>Result</code> 类型，那么就说明可能会产生错误，因此需要对其进行处理。</p> <p><code>unwrap</code> 有打开的意思，需要从 <code>Result</code> 中提取数据，但是 <code>run</code> 函数没有返回值，因此也就不需要 <code>unwrap</code>，可以像下面这样解决这一问题。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">if</span> <span class="token keyword">let</span> <span class="token class-name">Err</span><span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    213. 

  213.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;程序运行出错：{}&quot;</span><span class="token punctuation">,</span> e<span class="token punctuation">)</span><span class="token punctuation">;</span>
    214. 

  214.         <span class="token namespace">process<span class="token punctuation">::</span></span><span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    215. 

  215. <span class="token punctuation">}</span>
    216. 

  216. </code></pre></div><p>下面我们将业务逻辑迁移到 <code>lib.rs</code> 中。</p> <p><code>lib.rs:</code></p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    217. 

  217. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span>error<span class="token punctuation">::</span></span><span class="token class-name">Error</span><span class="token punctuation">;</span>
    218. 

  218. 

  219. <span class="token keyword">pub</span> <span class="token keyword">fn</span> <span class="token function-definition function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">:</span> <span class="token class-name">Config</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token class-name">Box</span><span class="token operator">&lt;</span><span class="token keyword">dyn</span> <span class="token class-name">Error</span><span class="token operator">&gt;&gt;</span> <span class="token punctuation">{</span>
    220. 

  220.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token operator">?</span><span class="token punctuation">;</span>
    221. 

  221.     <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;文件内容:\n{}&quot;</span><span class="token punctuation">,</span> content<span class="token punctuation">)</span><span class="token punctuation">;</span>
    222. 

  222.     <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    223. 

  223. <span class="token punctuation">}</span>
    224. 

  224. 

  225. <span class="token keyword">pub</span> <span class="token keyword">struct</span> <span class="token type-definition class-name">Config</span> <span class="token punctuation">{</span>
    226. 

  226.     <span class="token keyword">pub</span> search_string<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    227. 

  227.     <span class="token keyword">pub</span> filename<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    228. 

  228. <span class="token punctuation">}</span>
    229. 

  229. 

  230. <span class="token keyword">impl</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    231. 

  231.     <span class="token keyword">pub</span> <span class="token keyword">fn</span> <span class="token function-definition function">new</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token class-name">Config</span><span class="token punctuation">,</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    232. 

  232.         <span class="token keyword">if</span> args<span class="token punctuation">.</span><span class="token function">len</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">3</span> <span class="token punctuation">{</span>
    233. 

  233.             <span class="token keyword">return</span> <span class="token class-name">Err</span><span class="token punctuation">(</span><span class="token string">&quot;输入参数错误，请输入两个参数。&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    234. 

  234.         <span class="token punctuation">}</span>
    235. 

  235.         <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    236. 

  236.         <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    237. 

  237.         <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token class-name">Config</span> <span class="token punctuation">{</span>
    238. 

  238.             search_string<span class="token punctuation">,</span>
    239. 

  239.             filename<span class="token punctuation">,</span>
    240. 

  240.         <span class="token punctuation">}</span><span class="token punctuation">)</span>
    241. 

  241.     <span class="token punctuation">}</span>
    242. 

  242. <span class="token punctuation">}</span>
    243. 

  243. </code></pre></div><p><code>main.rs:</code></p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">minigrep<span class="token punctuation">::</span></span><span class="token class-name">Config</span><span class="token punctuation">;</span>
    244. 

  244. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    245. 

  245. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>process<span class="token punctuation">;</span>
    246. 

  246. 

  247. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    248. 

  248.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    249. 

  249. 

  250.     <span class="token keyword">let</span> config <span class="token operator">=</span> <span class="token class-name">Config</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">unwrap_or_else</span><span class="token punctuation">(</span><span class="token closure-params"><span class="token closure-punctuation punctuation">|</span>err<span class="token closure-punctuation punctuation">|</span></span> <span class="token punctuation">{</span>
    251. 

  251.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;参数解析错误：{}&quot;</span><span class="token punctuation">,</span> err<span class="token punctuation">)</span><span class="token punctuation">;</span>
    252. 

  252.         <span class="token namespace">process<span class="token punctuation">::</span></span><span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    253. 

  253.     <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    254. 

  254. 

  255.     <span class="token keyword">if</span> <span class="token keyword">let</span> <span class="token class-name">Err</span><span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token namespace">minigrep<span class="token punctuation">::</span></span><span class="token function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    256. 

  256.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;程序运行出错：{}&quot;</span><span class="token punctuation">,</span> e<span class="token punctuation">)</span><span class="token punctuation">;</span>
    257. 

  257.         <span class="token namespace">process<span class="token punctuation">::</span></span><span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    258. 

  258.     <span class="token punctuation">}</span>
    259. 

  259. <span class="token punctuation">}</span>
    260. 

  260. </code></pre></div><p>要记得所有函数和结构体以及字段前都要加 <code>pub</code>，这样才能让其他 <code>crate</code> 才能进行调用。这样 <code>lib crate</code> 就有了一套公共的可用于测试的 API。</p> <p>重构到这里就基本完成了，下面就要来编写测试了。</p> <h2 id="四、使用-tdd-测试驱动开发-开发库功能"><a href="#四、使用-tdd-测试驱动开发-开发库功能" class="header-anchor">#</a> 四、使用 TDD（测试驱动开发）开发库功能</h2> <p>测试驱动开发 TDD (Test-Driven Development)</p> <ul><li>编写一个会失败的测试，运行该测试，确保它是按照预期的原因失败</li> <li>编写或修改刚好足够的代码，让新测试通过</li> <li>重构刚刚添加或修改的代码，确保测试会始终通过</li> <li>返回步骤1，继续</li></ul> <p>测试驱动开发能够对代码的设计起到指导和帮助的作用，先编写测试，然后再编写能够通过测试的代码，也能保证开发过程中能够保持测试较高的覆盖率。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">fn</span> <span class="token function-definition function">search</span><span class="token operator">&lt;</span><span class="token lifetime-annotation symbol">'a</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>query<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token punctuation">,</span> content<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    261. 

  261.     <span class="token keyword">let</span> <span class="token keyword">mut</span> vec <span class="token operator">=</span> <span class="token class-name">Vec</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    262. 

  262.     <span class="token keyword">for</span> lines <span class="token keyword">in</span> content<span class="token punctuation">.</span><span class="token function">lines</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    263. 

  263.         <span class="token keyword">if</span> lines<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>query<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    264. 

  264.             vec<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>lines<span class="token punctuation">)</span><span class="token punctuation">;</span>
    265. 

  265.         <span class="token punctuation">}</span>
    266. 

  266.     <span class="token punctuation">}</span>
    267. 

  267.     vec
    268. 

  268. <span class="token punctuation">}</span>
    269. 

  269. 

  270. <span class="token attribute attr-name">#[cfg(test)]</span>
    271. 

  271. <span class="token keyword">mod</span> <span class="token module-declaration namespace">test</span> <span class="token punctuation">{</span>
    272. 

  272.     <span class="token attribute attr-name">#[test]</span>
    273. 

  273.     <span class="token keyword">fn</span> <span class="token function-definition function">one_result</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    274. 

  274.         <span class="token keyword">use</span> <span class="token keyword">super</span><span class="token punctuation">::</span><span class="token operator">*</span><span class="token punctuation">;</span>
    275. 

  275.         <span class="token keyword">let</span> query <span class="token operator">=</span> <span class="token string">&quot;Lakers&quot;</span><span class="token punctuation">;</span>
    276. 

  276.         <span class="token keyword">let</span> contents <span class="token operator">=</span> <span class="token string">&quot;\
    277. 

  277. Rust OK,
    278. 

  278. Paul, James, Lakers.
    279. 

  279. What a wonderful day!&quot;</span><span class="token punctuation">;</span>
    280. 

  280.         <span class="token macro property">assert_eq!</span><span class="token punctuation">(</span><span class="token macro property">vec!</span><span class="token punctuation">[</span><span class="token string">&quot;Paul, James, Lakers.&quot;</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token function">search</span><span class="token punctuation">(</span>query<span class="token punctuation">,</span> contents<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    281. 

  281.     <span class="token punctuation">}</span>
    282. 

  282. <span class="token punctuation">}</span>
    283. 

  283. </code></pre></div><p>注意 <code>search</code> 函数中返回的引用的生命周期与 <code>content</code> 有关，而与 <code>query</code> 无关。<code>content.lines()</code> 函数返回一个的迭代器，取出文件中的每一行。这样测试代码就完成了，运行测试也是成功的。</p> <div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ cargo test        
    284. 

  284.    <span class="token class-name">Compiling</span> minigrep v0<span class="token number">.1</span><span class="token punctuation">.</span><span class="token number">0</span> <span class="token punctuation">(</span><span class="token operator">/</span>home<span class="token operator">/</span>cherry<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep<span class="token punctuation">)</span>
    285. 

  285.     <span class="token class-name">Finished</span> test <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>36s
    286. 

  286.      <span class="token class-name">Running</span> <span class="token function">unittests</span> <span class="token punctuation">(</span>target<span class="token operator">/</span>debug<span class="token operator">/</span>deps<span class="token operator">/</span>minigrep<span class="token operator">-</span>662cb87b3d895995<span class="token punctuation">)</span>
    287. 

  287. 

  288. running <span class="token number">1</span> test
    289. 

  289. test <span class="token namespace">test<span class="token punctuation">::</span></span>one_result <span class="token punctuation">...</span> ok
    290. 

  290. 

  291. test result<span class="token punctuation">:</span> ok<span class="token punctuation">.</span> <span class="token number">1</span> passed<span class="token punctuation">;</span> <span class="token number">0</span> failed<span class="token punctuation">;</span> <span class="token number">0</span> ignored<span class="token punctuation">;</span> <span class="token number">0</span> measured<span class="token punctuation">;</span> <span class="token number">0</span> filtered out<span class="token punctuation">;</span> finished <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    292. 

  292. 

  293.      <span class="token class-name">Running</span> <span class="token function">unittests</span> <span class="token punctuation">(</span>target<span class="token operator">/</span>debug<span class="token operator">/</span>deps<span class="token operator">/</span>minigrep<span class="token operator">-</span>33abce92ed029d2f<span class="token punctuation">)</span>
    294. 

  294. 

  295. running <span class="token number">0</span> tests
    296. 

  296. 

  297. test result<span class="token punctuation">:</span> ok<span class="token punctuation">.</span> <span class="token number">0</span> passed<span class="token punctuation">;</span> <span class="token number">0</span> failed<span class="token punctuation">;</span> <span class="token number">0</span> ignored<span class="token punctuation">;</span> <span class="token number">0</span> measured<span class="token punctuation">;</span> <span class="token number">0</span> filtered out<span class="token punctuation">;</span> finished <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    298. 

  298. 

  299.    <span class="token class-name">Doc</span><span class="token operator">-</span>tests minigrep
    300. 

  300. 

  301. running <span class="token number">0</span> tests
    302. 

  302. 

  303. test result<span class="token punctuation">:</span> ok<span class="token punctuation">.</span> <span class="token number">0</span> passed<span class="token punctuation">;</span> <span class="token number">0</span> failed<span class="token punctuation">;</span> <span class="token number">0</span> ignored<span class="token punctuation">;</span> <span class="token number">0</span> measured<span class="token punctuation">;</span> <span class="token number">0</span> filtered out<span class="token punctuation">;</span> finished <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    304. 

  304. </code></pre></div><p>然后修改 <code>run</code> 函数并运行 <code>cargo run</code>。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">pub</span> <span class="token keyword">fn</span> <span class="token function-definition function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">:</span> <span class="token class-name">Config</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token class-name">Box</span><span class="token operator">&lt;</span><span class="token keyword">dyn</span> <span class="token class-name">Error</span><span class="token operator">&gt;&gt;</span> <span class="token punctuation">{</span>
    305. 

  305.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token operator">?</span><span class="token punctuation">;</span>
    306. 

  306.     <span class="token comment">// println!(&quot;文件内容:\n{}&quot;, content);</span>
    307. 

  307.     <span class="token keyword">for</span> line <span class="token keyword">in</span> <span class="token function">search</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>config<span class="token punctuation">.</span>search_string<span class="token punctuation">,</span> <span class="token operator">&amp;</span>content<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    308. 

  308.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;{}&quot;</span><span class="token punctuation">,</span> line<span class="token punctuation">)</span><span class="token punctuation">;</span>
    309. 

  309.     <span class="token punctuation">}</span>
    310. 

  310.     <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    311. 

  311. <span class="token punctuation">}</span>
    312. 

  312. </code></pre></div><div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ cargo run is poem 
    313. 

  313.     <span class="token class-name">Finished</span> dev <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    314. 

  314.      <span class="token class-name">Running</span> `target<span class="token operator">/</span>debug<span class="token operator">/</span>minigrep is poem`
    315. 

  315. <span class="token class-name">Life</span> is a broken<span class="token operator">-</span>winged bird
    316. 

  316. <span class="token class-name">Life</span> is a barren field
    317. 

  317. </code></pre></div><h2 id="五、使用环境变量"><a href="#五、使用环境变量" class="header-anchor">#</a> 五、使用环境变量</h2> <p>这一部分使用环境变量来实现配置选项（例如是否忽略大小写等）。</p> <p>我们首先编写一个测试：</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token attribute attr-name">#[test]</span>
    318. 

  318. <span class="token keyword">fn</span> <span class="token function-definition function">case_insensitive</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    319. 

  319.     <span class="token keyword">let</span> query <span class="token operator">=</span> <span class="token string">&quot;LakErS&quot;</span><span class="token punctuation">;</span>
    320. 

  320.     <span class="token keyword">let</span> contents <span class="token operator">=</span> <span class="token string">&quot;
    321. 

  321. Rust OK,
    322. 

  322. Paul, James, Lakers.
    323. 

  323. What a wonderful day!
    324. 

  324. blakers championship&quot;</span><span class="token punctuation">;</span>
    325. 

  325.     <span class="token macro property">assert_eq!</span><span class="token punctuation">(</span><span class="token macro property">vec!</span><span class="token punctuation">[</span><span class="token string">&quot;Paul, James, Lakers.&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;blakers championship&quot;</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token function">search_case_insensitive</span><span class="token punctuation">(</span>query<span class="token punctuation">,</span> contents<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    326. 

  326. <span class="token punctuation">}</span>
    327. 

  327. </code></pre></div><p>然后编写 <code>search_case_insensitive</code> 函数：</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">fn</span> <span class="token function-definition function">search_case_insensitive</span><span class="token operator">&lt;</span><span class="token lifetime-annotation symbol">'a</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>query<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token punctuation">,</span> content<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    328. 

  328.     <span class="token keyword">let</span> <span class="token keyword">mut</span> vec <span class="token operator">=</span> <span class="token class-name">Vec</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    329. 

  329.     <span class="token keyword">let</span> query <span class="token operator">=</span> query<span class="token punctuation">.</span><span class="token function">to_lowercase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    330. 

  330.     <span class="token keyword">for</span> lines <span class="token keyword">in</span> content<span class="token punctuation">.</span><span class="token function">lines</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    331. 

  331.         <span class="token keyword">if</span> lines<span class="token punctuation">.</span><span class="token function">to_lowercase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>query<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    332. 

  332.             vec<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>lines<span class="token punctuation">)</span><span class="token punctuation">;</span>
    333. 

  333.         <span class="token punctuation">}</span>
    334. 

  334.     <span class="token punctuation">}</span>
    335. 

  335.     vec
    336. 

  336. <span class="token punctuation">}</span>
    337. 

  337. </code></pre></div><p>其思路就是将查询的字符串和文件中的都转化成小写。</p> <p>然后我们在 <code>run</code> 函数中加入如下逻辑。</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">let</span> result <span class="token operator">=</span> <span class="token keyword">if</span> config<span class="token punctuation">.</span>case_sensitive <span class="token punctuation">{</span>
    338. 

  338.     <span class="token function">search</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>config<span class="token punctuation">.</span>search_string<span class="token punctuation">,</span> <span class="token operator">&amp;</span>content<span class="token punctuation">)</span>
    339. 

  339. <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    340. 

  340.     <span class="token function">search_case_insensitive</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>config<span class="token punctuation">.</span>search_string<span class="token punctuation">,</span> <span class="token operator">&amp;</span>content<span class="token punctuation">)</span>
    341. 

  341. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    342. 

  342. </code></pre></div><p>结构体的 <code>new</code> 函数也需要修改：</p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">pub</span> <span class="token keyword">fn</span> <span class="token function-definition function">new</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token class-name">Config</span><span class="token punctuation">,</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    343. 

  343.     <span class="token keyword">if</span> args<span class="token punctuation">.</span><span class="token function">len</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">3</span> <span class="token punctuation">{</span>
    344. 

  344.         <span class="token keyword">return</span> <span class="token class-name">Err</span><span class="token punctuation">(</span><span class="token string">&quot;输入参数错误，请输入两个参数。&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    345. 

  345.     <span class="token punctuation">}</span>
    346. 

  346.     <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    347. 

  347.     <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    348. 

  348.     <span class="token keyword">let</span> case_sensitive <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">var</span><span class="token punctuation">(</span><span class="token string">&quot;CASE_INSENSITIVE&quot;</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">is_err</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    349. 

  349.     <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token class-name">Config</span> <span class="token punctuation">{</span>
    350. 

  350.         search_string<span class="token punctuation">,</span>
    351. 

  351.         filename<span class="token punctuation">,</span>
    352. 

  352.         case_sensitive
    353. 

  353.     <span class="token punctuation">}</span><span class="token punctuation">)</span>
    354. 

  354. <span class="token punctuation">}</span>
    355. 

  355. </code></pre></div><p><code>env::var()</code> 函数返回的是 <code>Result</code> 枚举，若环境中有 <code>CASE_INSENSITIVE</code> 定义或者赋值，那么就会返回 <code>Ok</code> 中的值，我们这里只需要判断是否为 <code>Err</code> 即可。</p> <div class="language-rust extra-class"><pre class="language-rust"><code>➜  ~<span class="token operator">/</span>code<span class="token operator">/</span>rust<span class="token operator">/</span>minigrep git<span class="token punctuation">:</span><span class="token punctuation">(</span>master<span class="token punctuation">)</span> ✗ <span class="token constant">CASE_INSENSITIVE</span><span class="token operator">=</span><span class="token number">1</span> cargo run to poem
    356. 

  356.     <span class="token class-name">Finished</span> dev <span class="token punctuation">[</span>unoptimized <span class="token operator">+</span> debuginfo<span class="token punctuation">]</span> <span class="token function">target</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span> <span class="token keyword">in</span> <span class="token number">0</span><span class="token punctuation">.</span>00s
    357. 

  357.      <span class="token class-name">Running</span> `target<span class="token operator">/</span>debug<span class="token operator">/</span>minigrep to poem`
    358. 

  358. <span class="token class-name">Hold</span> fast to dreams
    359. 

  359. <span class="token class-name">Hold</span> fast to dreams
    360. 

  360. <span class="token class-name">To</span> see a world <span class="token keyword">in</span> a grain of sand<span class="token punctuation">,</span>
    361. 

  361. </code></pre></div><h2 id="六、将错误消息写进标准错误而不是标准输出"><a href="#六、将错误消息写进标准错误而不是标准输出" class="header-anchor">#</a> 六、将错误消息写进标准错误而不是标准输出</h2> <p>当前我们都将错误信息输出到终端上，而大多数终端提供两种输出，一个是标准输出（stdout，println!），另一个叫标准错误（stderr，eprintln!）。</p> <p>我们将打印错误信息的 <code>println!</code> 改成 <code>eprintln!</code> 即可，然后运行 <code>cargo run &gt; output</code>，错误信息便不会输出到文件中，而是打印在终端了。</p> <h2 id="七、完整代码"><a href="#七、完整代码" class="header-anchor">#</a> 七、完整代码</h2> <p><strong>main.rs:</strong></p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">minigrep<span class="token punctuation">::</span></span><span class="token class-name">Config</span><span class="token punctuation">;</span>
    362. 

  362. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    363. 

  363. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>process<span class="token punctuation">;</span>
    364. 

  364. 

  365. <span class="token keyword">fn</span> <span class="token function-definition function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    366. 

  366.     <span class="token keyword">let</span> args<span class="token punctuation">:</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token class-name">String</span><span class="token operator">&gt;</span> <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">args</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    367. 

  367. 

  368.     <span class="token keyword">let</span> config <span class="token operator">=</span> <span class="token class-name">Config</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">unwrap_or_else</span><span class="token punctuation">(</span><span class="token closure-params"><span class="token closure-punctuation punctuation">|</span>err<span class="token closure-punctuation punctuation">|</span></span> <span class="token punctuation">{</span>
    369. 

  369.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;参数解析错误：{}&quot;</span><span class="token punctuation">,</span> err<span class="token punctuation">)</span><span class="token punctuation">;</span>
    370. 

  370.         <span class="token namespace">process<span class="token punctuation">::</span></span><span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    371. 

  371.     <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    372. 

  372. 

  373.     <span class="token keyword">if</span> <span class="token keyword">let</span> <span class="token class-name">Err</span><span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token namespace">minigrep<span class="token punctuation">::</span></span><span class="token function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    374. 

  374.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;程序运行出错：{}&quot;</span><span class="token punctuation">,</span> e<span class="token punctuation">)</span><span class="token punctuation">;</span>
    375. 

  375.         <span class="token namespace">process<span class="token punctuation">::</span></span><span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    376. 

  376.     <span class="token punctuation">}</span>
    377. 

  377. <span class="token punctuation">}</span>
    378. 

  378. </code></pre></div><p><strong>lib.rs:</strong></p> <div class="language-rust extra-class"><pre class="language-rust"><code><span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span>error<span class="token punctuation">::</span></span><span class="token class-name">Error</span><span class="token punctuation">;</span>
    379. 

  379. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>fs<span class="token punctuation">;</span>
    380. 

  380. <span class="token keyword">use</span> <span class="token namespace">std<span class="token punctuation">::</span></span>env<span class="token punctuation">;</span>
    381. 

  381. 

  382. <span class="token keyword">pub</span> <span class="token keyword">fn</span> <span class="token function-definition function">run</span><span class="token punctuation">(</span>config<span class="token punctuation">:</span> <span class="token class-name">Config</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token class-name">Box</span><span class="token operator">&lt;</span><span class="token keyword">dyn</span> <span class="token class-name">Error</span><span class="token operator">&gt;&gt;</span> <span class="token punctuation">{</span>
    383. 

  383.     <span class="token keyword">let</span> content <span class="token operator">=</span> <span class="token namespace">fs<span class="token punctuation">::</span></span><span class="token function">read_to_string</span><span class="token punctuation">(</span>config<span class="token punctuation">.</span>filename<span class="token punctuation">)</span><span class="token operator">?</span><span class="token punctuation">;</span>
    384. 

  384.     <span class="token comment">// println!(&quot;文件内容:\n{}&quot;, content);</span>
    385. 

  385.     <span class="token keyword">let</span> result <span class="token operator">=</span> <span class="token keyword">if</span> config<span class="token punctuation">.</span>case_sensitive <span class="token punctuation">{</span>
    386. 

  386.         <span class="token function">search</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>config<span class="token punctuation">.</span>search_string<span class="token punctuation">,</span> <span class="token operator">&amp;</span>content<span class="token punctuation">)</span>
    387. 

  387.     <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    388. 

  388.         <span class="token function">search_case_insensitive</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>config<span class="token punctuation">.</span>search_string<span class="token punctuation">,</span> <span class="token operator">&amp;</span>content<span class="token punctuation">)</span>
    389. 

  389.     <span class="token punctuation">}</span><span class="token punctuation">;</span>
    390. 

  390.     <span class="token keyword">for</span> line <span class="token keyword">in</span> result <span class="token punctuation">{</span>
    391. 

  391.         <span class="token macro property">println!</span><span class="token punctuation">(</span><span class="token string">&quot;{}&quot;</span><span class="token punctuation">,</span> line<span class="token punctuation">)</span><span class="token punctuation">;</span>
    392. 

  392.     <span class="token punctuation">}</span>
    393. 

  393.     <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    394. 

  394. <span class="token punctuation">}</span>
    395. 

  395. 

  396. <span class="token keyword">pub</span> <span class="token keyword">struct</span> <span class="token type-definition class-name">Config</span> <span class="token punctuation">{</span>
    397. 

  397.     <span class="token keyword">pub</span> search_string<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    398. 

  398.     <span class="token keyword">pub</span> filename<span class="token punctuation">:</span> <span class="token class-name">String</span><span class="token punctuation">,</span>
    399. 

  399.     <span class="token keyword">pub</span> case_sensitive<span class="token punctuation">:</span> <span class="token keyword">bool</span>
    400. 

  400. <span class="token punctuation">}</span>
    401. 

  401. 

  402. <span class="token keyword">impl</span> <span class="token class-name">Config</span> <span class="token punctuation">{</span>
    403. 

  403.     <span class="token keyword">pub</span> <span class="token keyword">fn</span> <span class="token function-definition function">new</span><span class="token punctuation">(</span>args<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token punctuation">[</span><span class="token class-name">String</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Result</span><span class="token operator">&lt;</span><span class="token class-name">Config</span><span class="token punctuation">,</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    404. 

  404.         <span class="token keyword">if</span> args<span class="token punctuation">.</span><span class="token function">len</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">3</span> <span class="token punctuation">{</span>
    405. 

  405.             <span class="token keyword">return</span> <span class="token class-name">Err</span><span class="token punctuation">(</span><span class="token string">&quot;输入参数错误，请输入两个参数。&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    406. 

  406.         <span class="token punctuation">}</span>
    407. 

  407.         <span class="token keyword">let</span> search_string <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    408. 

  408.         <span class="token keyword">let</span> filename <span class="token operator">=</span> args<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    409. 

  409.         <span class="token keyword">let</span> case_sensitive <span class="token operator">=</span> <span class="token namespace">env<span class="token punctuation">::</span></span><span class="token function">var</span><span class="token punctuation">(</span><span class="token string">&quot;CASE_INSENSITIVE&quot;</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">is_err</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    410. 

  410.         <span class="token class-name">Ok</span><span class="token punctuation">(</span><span class="token class-name">Config</span> <span class="token punctuation">{</span>
    411. 

  411.             search_string<span class="token punctuation">,</span>
    412. 

  412.             filename<span class="token punctuation">,</span>
    413. 

  413.             case_sensitive
    414. 

  414.         <span class="token punctuation">}</span><span class="token punctuation">)</span>
    415. 

  415.     <span class="token punctuation">}</span>
    416. 

  416. <span class="token punctuation">}</span>
    417. 

  417. 

  418. <span class="token keyword">fn</span> <span class="token function-definition function">search</span><span class="token operator">&lt;</span><span class="token lifetime-annotation symbol">'a</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>query<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token punctuation">,</span> content<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    419. 

  419.     <span class="token keyword">let</span> <span class="token keyword">mut</span> vec <span class="token operator">=</span> <span class="token class-name">Vec</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    420. 

  420.     <span class="token keyword">for</span> lines <span class="token keyword">in</span> content<span class="token punctuation">.</span><span class="token function">lines</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    421. 

  421.         <span class="token keyword">if</span> lines<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>query<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    422. 

  422.             vec<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>lines<span class="token punctuation">)</span><span class="token punctuation">;</span>
    423. 

  423.         <span class="token punctuation">}</span>
    424. 

  424.     <span class="token punctuation">}</span>
    425. 

  425.     vec
    426. 

  426. <span class="token punctuation">}</span>
    427. 

  427. 

  428. <span class="token keyword">fn</span> <span class="token function-definition function">search_case_insensitive</span><span class="token operator">&lt;</span><span class="token lifetime-annotation symbol">'a</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>query<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token keyword">str</span><span class="token punctuation">,</span> content<span class="token punctuation">:</span> <span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token punctuation">)</span> <span class="token punctuation">-&gt;</span> <span class="token class-name">Vec</span><span class="token operator">&lt;</span><span class="token operator">&amp;</span><span class="token lifetime-annotation symbol">'a</span> <span class="token keyword">str</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    429. 

  429.     <span class="token keyword">let</span> <span class="token keyword">mut</span> vec <span class="token operator">=</span> <span class="token class-name">Vec</span><span class="token punctuation">::</span><span class="token function">new</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    430. 

  430.     <span class="token keyword">let</span> query <span class="token operator">=</span> query<span class="token punctuation">.</span><span class="token function">to_lowercase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    431. 

  431.     <span class="token keyword">for</span> lines <span class="token keyword">in</span> content<span class="token punctuation">.</span><span class="token function">lines</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    432. 

  432.         <span class="token keyword">if</span> lines<span class="token punctuation">.</span><span class="token function">to_lowercase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>query<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    433. 

  433.             vec<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>lines<span class="token punctuation">)</span><span class="token punctuation">;</span>
    434. 

  434.         <span class="token punctuation">}</span>
    435. 

  435.     <span class="token punctuation">}</span>
    436. 

  436.     vec
    437. 

  437. <span class="token punctuation">}</span>
    438. 

  438. 

  439. <span class="token attribute attr-name">#[cfg(test)]</span>
    440. 

  440. <span class="token keyword">mod</span> <span class="token module-declaration namespace">test</span> <span class="token punctuation">{</span>
    441. 

  441.     <span class="token keyword">use</span> <span class="token keyword">super</span><span class="token punctuation">::</span><span class="token operator">*</span><span class="token punctuation">;</span>
    442. 

  442.     <span class="token attribute attr-name">#[test]</span>
    443. 

  443.     <span class="token keyword">fn</span> <span class="token function-definition function">one_result</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    444. 

  444.         <span class="token keyword">let</span> query <span class="token operator">=</span> <span class="token string">&quot;Lakers&quot;</span><span class="token punctuation">;</span>
    445. 

  445.         <span class="token keyword">let</span> contents <span class="token operator">=</span> <span class="token string">&quot;\
    446. 

  446. Rust OK,
    447. 

  447. Paul, James, Lakers.
    448. 

  448. What a wonderful day!&quot;</span><span class="token punctuation">;</span>
    449. 

  449.         <span class="token macro property">assert_eq!</span><span class="token punctuation">(</span><span class="token macro property">vec!</span><span class="token punctuation">[</span><span class="token string">&quot;Paul, James, Lakers.&quot;</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token function">search</span><span class="token punctuation">(</span>query<span class="token punctuation">,</span> contents<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    450. 

  450.     <span class="token punctuation">}</span>
    451. 

  451. 

  452.     <span class="token attribute attr-name">#[test]</span>
    453. 

  453.     <span class="token keyword">fn</span> <span class="token function-definition function">case_insensitive</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    454. 

  454.         <span class="token keyword">let</span> query <span class="token operator">=</span> <span class="token string">&quot;LakErS&quot;</span><span class="token punctuation">;</span>
    455. 

  455.         <span class="token keyword">let</span> contents <span class="token operator">=</span> <span class="token string">&quot;
    456. 

  456. Rust OK,
    457. 

  457. Paul, James, Lakers.
    458. 

  458. What a wonderful day!
    459. 

  459. blakers championship&quot;</span><span class="token punctuation">;</span>
    460. 

  460.         <span class="token macro property">assert_eq!</span><span class="token punctuation">(</span>
    461. 

  461.             <span class="token macro property">vec!</span><span class="token punctuation">[</span><span class="token string">&quot;Paul, James, Lakers.&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;blakers championship&quot;</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    462. 

  462.             <span class="token function">search_case_insensitive</span><span class="token punctuation">(</span>query<span class="token punctuation">,</span> contents<span class="token punctuation">)</span>
    463. 

  463.         <span class="token punctuation">)</span><span class="token punctuation">;</span>
    464. 

  464.     <span class="token punctuation">}</span>
    465. 

  465. <span class="token punctuation">}</span>
    466. 

  466. </code></pre></div><h2 id="八、案例-代码统计"><a href="#八、案例-代码统计" class="header-anchor">#</a> 八、案例：代码统计</h2> <h3 id="_8-1-基本功能介绍"><a href="#_8-1-基本功能介绍" class="header-anchor">#</a> 8.1 基本功能介绍</h3> <p>代码统计以给定的输入参数作为统计对象（可以是文件或文件夹），根据文件后缀名统计代码所使用的语言（暂定只统计 C、C/C++ 头文件、C++、Java、Python、Rust、汇编语言、makefile 脚本），然后统计每一种代码文件的有效代码行数、注释行和空行。没有后缀名的文件默认不进行统计。</p> <h3 id="_8-2-可拓展功能"><a href="#_8-2-可拓展功能" class="header-anchor">#</a> 8.2 可拓展功能</h3> <ul><li>丰富统计的语言种类</li> <li>命令行中利用参数指定要统计的语言，只统计指定的语言</li> <li>统计若干种编程语言的有效代码行数，空行和注释</li> <li>可以对单个文件、多个文件进行统计</li> <li>支持一些参数，例如：排除某些文件或文件夹</li> <li>可以对文件夹进行递归统计</li> <li>对压缩文件包进行递归统计</li> <li>直观展示统计结果</li> <li>将统计结果导出为图片或 PDF</li> <li>利用多线程加速代码统计</li></ul> <h3 id="_8-3-代码仓库及说明"><a href="#_8-3-代码仓库及说明" class="header-anchor">#</a> 8.3 代码仓库及说明</h3> <p>由于笔者时间有限，目前只完成了一些简单的功能，但是完全可用。2022 年 10 月之后就没有再写了，不过后续可能会有计划再完善该项目，目前该项目的代码在 <a href="https://github.com/CherryYang05/mcloc" target="_blank" rel="noopener noreferrer">Github仓库<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> 中，初学者可以以此巩固一下基本语法，如果有兴趣可以帮助完善一下功能，编程老鸟就可以完全不必理会这个项目（笑）。</p></div> <footer class="page-edit"><!----> <!----></footer> <!----> </main></div><div class="global-ui"></div></div>
    467. 

  467.     <script src="/rust_camp_tutorial/assets/js/app.d7ab8f65.js" defer></script><script src="/rust_camp_tutorial/assets/js/2.3dc1b8de.js" defer></script><script src="/rust_camp_tutorial/assets/js/1.7f771cfb.js" defer></script><script src="/rust_camp_tutorial/assets/js/27.928f1e6b.js" defer></script>
    468. 

  468.   </body>
    469. 

  469. </html>
    470.