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- (window.webpackJsonp=window.webpackJsonp||[]).push([[28],{309: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-二-结构体和枚举"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#rust-入门教程-二-结构体和枚举"}},[t._v("#")]),t._v(" Rust 入门教程（二）：结构体和枚举")]),t._v(" "),s("h2",{attrs:{id:"一、结构体的使用"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#一、结构体的使用"}},[t._v("#")]),t._v(" 一、结构体的使用")]),t._v(" "),s("h3",{attrs:{id:"_1-定义和实例化-struct"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1-定义和实例化-struct"}},[t._v("#")]),t._v(" 1. 定义和实例化 struct")]),t._v(" "),s("p",[t._v("例子：")]),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("struct")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token type-definition 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是不同的类型，是不同 tuple struct 的实例")]),t._v(" "),s("p",[s("strong",[t._v("Unit-Like Struct(没有任何字段)")])]),t._v(" "),s("p",[t._v("可以定义没有任何字段的 struct，叫做 "),s("code",[t._v("Unit-Like struct")]),t._v("，因为与 "),s("code",[t._v("()")]),t._v(" 和单元类型类似，适用于需要在某个类型上实现某个trait，但是在里面又没有想要存储的数据")]),t._v(" "),s("p",[s("strong",[t._v("struct 数据所有权")])]),t._v(" "),s("p",[t._v("再来看这个例子：")]),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("struct")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token type-definition class-name"}},[t._v("User")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n username"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n email"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n sign_in_count"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("usize")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n active"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("bool")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("这里的字段使用了 "),s("code",[t._v("String")]),t._v(" 而不是 "),s("code",[t._v("&str")]),t._v("，原因如下：")]),t._v(" "),s("ul",[s("li",[t._v("该 struct 实例拥有其所有的数据")]),t._v(" "),s("li",[t._v("只要 struct 实例是有效的，那么里面的字段数据也是有效的 struct 里也可以存放引用，但这需要使用生命周期（以后讲）")]),t._v(" "),s("li",[t._v("若字段为 "),s("code",[t._v("&str")]),t._v("，当其有效作用域小于该实例的作用域，该字段被清理时，实例未清理，访问该字段属于悬垂引用（类似野指针）")]),t._v(" "),s("li",[t._v("生命周期保证只要 struct 实例是有效的，那么里面的引用也是有效的")]),t._v(" "),s("li",[t._v("如果 struct 里面存储引用，而不使用生命周期，就会报错")])]),t._v(" "),s("h3",{attrs:{id:"_2-struct-例子"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-struct-例子"}},[t._v("#")]),t._v(" 2. struct 例子")]),t._v(" "),s("p",[t._v("一个简单的例子：计算长方形的面积")]),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("main")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" width "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("25")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" length "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("12")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" area "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("area_of_rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("width"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" length"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"The Area of Rectangle is {}."')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" area"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),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("area_of_rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("width"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("usize")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" length"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("usize")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("->")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("usize")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n width "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" length\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("上面这个例子很简单，但是长方形的长和宽没有联系起来，width 和 length 是两个分离的没有逻辑联系的变量，我们考虑用元组将其联系起来：")]),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("main")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" rect "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("25")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("12")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"The Area of Rectangle is {}."')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("area_of_rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("rect"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),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("area_of_rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("rect"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token type-definition class-name"}},[t._v("Rectangle")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n width"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("u32")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n length"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("u32")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition 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"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"The Area of Rectangle is {}."')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("area_of_rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("rect"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),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("area_of_rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("rect"),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 class-name"}},[t._v("Rectangle")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("->")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("u32")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n rect"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("length "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" rect"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("width\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("函数的参数使用结构体的借用，是为了不获得该实例的所有权，主函数在函数调用之后还可以继续使用该实例。")]),t._v(" "),s("p",[t._v("此时我们输出实例 "),s("code",[t._v("rect")]),t._v("，会报这样的错误："),s("code",[t._v("Rectangle doesn't implement std::fmt::Display")]),t._v("，即该结构体未实现 "),s("code",[t._v("Display")]),t._v(" 这个 trait，而 Rust 中很多类型都是实现了这个 trait，才能将其在终端打印出来。因为结构体这种比标量类型更加复杂，打印的类型的可能性很多，因此需要用户自定义实现 "),s("code",[t._v("Display")]),t._v("。")]),t._v(" "),s("p",[t._v("在报错的提示信息里，有个 note 提示我们可以使用 "),s("code",[t._v("{:?}")]),t._v(" (或 "),s("code",[t._v("{:#?}")]),t._v(")来打印信息:")]),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 macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"{:?}"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" rect"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])])]),s("p",[t._v("然而又出现了错误，这次的报错信息是："),s("code",[t._v("Rectangle doesn't implement Debug")]),t._v("，显然 "),s("code",[t._v("Debug")]),t._v(" 也是一种格式化方法，再看提示的 note："),s("code",[t._v("add #[derive(Debug)] to Rectangle or manually impl Debug for Rectangle")]),t._v("，我们在结构体前添加 "),s("code",[t._v("#[derive(Debug)]")]),t._v("，使得该结构体派生与 "),s("code",[t._v("Debug")]),t._v(" 这个 trait。")]),t._v(" "),s("p",[t._v("最终完整的程序如下：")]),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 attribute attr-name"}},[t._v("#[derive(Debug)]")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token type-definition class-name"}},[t._v("Rectangle")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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