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- (window.webpackJsonp=window.webpackJsonp||[]).push([[27],{308:function(t,s,a){"use strict";a.r(s);var n=a(14),e=Object(n.a)({},(function(){var t=this,s=t._self._c;return s("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[s("h1",{attrs:{id:"rust入门教程-九-实战演练-一个简单的-grep-程序"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#rust入门教程-九-实战演练-一个简单的-grep-程序"}},[t._v("#")]),t._v(" Rust入门教程（九）：实战演练：一个简单的 grep 程序")]),t._v(" "),s("blockquote",[s("p",[t._v("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。\n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。")])]),t._v(" "),s("p",[t._v("下面开始实战演示。")]),t._v(" "),s("h2",{attrs:{id:"一、接收命令行参数"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#一、接收命令行参数"}},[t._v("#")]),t._v(" 一、接收命令行参数")]),t._v(" "),s("p",[t._v("我们预计使用如下命令来执行该程序：")]),t._v(" "),s("div",{staticClass:"language-bash 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"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" dreams die\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Life")]),t._v(" is a broken"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("winged bird\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("That")]),t._v(" can never fly\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Hold")]),t._v(" fast to dreams\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("For")]),t._v(" when dreams go\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Life")]),t._v(" is a barren field\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Frozen")]),t._v(" only with snow\n\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("To")]),t._v(" see a world "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" a grain of sand"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("And")]),t._v(" a heaven "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" a wild flower"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Hold")]),t._v(" infinity "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" the palm of your hand"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("And")]),t._v(" eternity "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" an hour"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("\n")])])]),s("p",[t._v("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。")]),t._v(" "),s("h2",{attrs:{id:"三、重构-改进模块和错误处理"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#三、重构-改进模块和错误处理"}},[t._v("#")]),t._v(" 三、重构：改进模块和错误处理")]),t._v(" "),s("h3",{attrs:{id:"_3-1-四个问题提炼"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-四个问题提炼"}},[t._v("#")]),t._v(" 3.1 四个问题提炼")]),t._v(" "),s("p",[t._v("我们仔细观察一下目前的代码，主要有四个方面的问题。")]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("use")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token namespace"}},[t._v("std"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")])]),t._v("env"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("use")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token namespace"}},[t._v("std"),s("span",{pre:!0,attrs:{class:"token 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"),s("li",[t._v("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 "),s("code",[t._v("Out of bound")]),t._v(" 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 "),s("strong",[t._v("越界错误")]),t._v(" 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 "),s("code",[t._v("Out of bound")]),t._v("。")])]),t._v(" "),s("h3",{attrs:{id:"_3-2-二进制程序关注点分离的指导性原则"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-二进制程序关注点分离的指导性原则"}},[t._v("#")]),t._v(" 3.2 二进制程序关注点分离的指导性原则")]),t._v(" "),s("ul",[s("li",[t._v("将程序拆分为 "),s("code",[t._v("main.rs")]),t._v(" 和 "),s("code",[t._v("lib.rs")]),t._v("，将业务逻辑放入 "),s("code",[t._v("lib.rs")])]),t._v(" "),s("li",[t._v("当命令行解析逻辑较少时，将它放在 "),s("code",[t._v("main.rs")]),t._v(" 也行")]),t._v(" "),s("li",[t._v("当命令行解析逻辑变复杂时，需要将它从 "),s("code",[t._v("main.rs")]),t._v(" 提取到 "),s("code",[t._v("lib.rs")])])]),t._v(" "),s("p",[t._v("经过上述拆分，留在 "),s("code",[t._v("main")]),t._v(" 的功能有：")]),t._v(" "),s("ul",[s("li",[t._v("使用参数值调用命令行解析逻辑")]),t._v(" "),s("li",[t._v("进行其它配置")]),t._v(" "),s("li",[t._v("调用 "),s("code",[t._v("lib.rs")]),t._v(" 中的 "),s("code",[t._v("run")]),t._v(" 函数")]),t._v(" "),s("li",[t._v("处理 "),s("code",[t._v("run")]),t._v(" 函数可能出现的错误")])]),t._v(" "),s("p",[t._v("因此放在 "),s("code",[t._v("main.rs")]),t._v(" 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 "),s("code",[t._v("lib.rs")]),t._v(" 中也方便进行功能测试。")]),t._v(" "),s("p",[t._v("针对上面说的四个方面的问题，我们逐一进行解决。")]),t._v(" "),s("p",[s("strong",[t._v("1. 拆分出命令行参数提取功能")])]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("use")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token namespace"}},[t._v("std"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")])]),t._v("env"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("use")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("code",[t._v("Config")]),t._v(" 结构体对象，该结构体需要占用所有权，因此会报错。")]),t._v(" "),s("p",[t._v("这里用一个简单的方法来处理，就是创建 "),s("code",[t._v("args[1]")]),t._v(" 和 "),s("code",[t._v("args[2]")]),t._v(" 的两个副本，尽管这样会损失性能。")]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition function"}},[t._v("parse_config")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("args"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" 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