<!DOCTYPE HTML>
< html lang = "zh-CN" class = "light sidebar-visible" dir = "ltr" >
< head >
<!-- Book generated using mdBook -->
< meta charset = "UTF-8" >
< title > 不仅仅是 Hello world - Rust语言圣经(Rust Course)< / title >
<!-- Custom HTML head -->
< meta name = "description" content = "" >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "theme-color" content = "#ffffff" >
< link rel = "icon" href = "../favicon-de23e50b.svg" >
< link rel = "shortcut icon" href = "../favicon-8114d1fc.png" >
< link rel = "stylesheet" href = "../css/variables-8adf115d.css" >
< link rel = "stylesheet" href = "../css/general-2459343d.css" >
< link rel = "stylesheet" href = "../css/chrome-ae938929.css" >
< link rel = "stylesheet" href = "../css/print-9e4910d8.css" media = "print" >
<!-- Fonts -->
< link rel = "stylesheet" href = "../fonts/fonts-9644e21d.css" >
<!-- Highlight.js Stylesheets -->
< link rel = "stylesheet" id = "mdbook-highlight-css" href = "../highlight-493f70e1.css" >
< link rel = "stylesheet" id = "mdbook-tomorrow-night-css" href = "../tomorrow-night-4c0ae647.css" >
< link rel = "stylesheet" id = "mdbook-ayu-highlight-css" href = "../ayu-highlight-3fdfc3ac.css" >
<!-- Custom theme stylesheets -->
< link rel = "stylesheet" href = "../theme/style-234bffbf.css" >
<!-- Provide site root and default themes to javascript -->
< script >
const path_to_root = "../";
const default_light_theme = "light";
const default_dark_theme = "navy";
window.path_to_searchindex_js = "../searchindex-4a1a74fa.js";
< / script >
<!-- Start loading toc.js asap -->
< script src = "../toc-42887675.js" > < / script >
< / head >
< body >
< div id = "mdbook-help-container" >
< div id = "mdbook-help-popup" >
< h2 class = "mdbook-help-title" > Keyboard shortcuts< / h2 >
< div >
< p > Press < kbd > ←< / kbd > or < kbd > →< / kbd > to navigate between chapters< / p >
< p > Press < kbd > S< / kbd > or < kbd > /< / kbd > to search in the book< / p >
< p > Press < kbd > ?< / kbd > to show this help< / p >
< p > Press < kbd > Esc< / kbd > to hide this help< / p >
< / div >
< / div >
< / div >
< div id = "mdbook-body-container" >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script >
try {
let theme = localStorage.getItem('mdbook-theme');
let sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script >
const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
let theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
const html = document.documentElement;
html.classList.remove('light')
html.classList.add(theme);
html.classList.add("js");
< / script >
< input type = "checkbox" id = "mdbook-sidebar-toggle-anchor" class = "hidden" >
<!-- Hide / unhide sidebar before it is displayed -->
< script >
let sidebar = null;
const sidebar_toggle = document.getElementById("mdbook-sidebar-toggle-anchor");
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
} else {
sidebar = 'hidden';
sidebar_toggle.checked = false;
}
if (sidebar === 'visible') {
sidebar_toggle.checked = true;
} else {
html.classList.remove('sidebar-visible');
}
< / script >
< nav id = "mdbook-sidebar" class = "sidebar" aria-label = "Table of contents" >
<!-- populated by js -->
< mdbook-sidebar-scrollbox class = "sidebar-scrollbox" > < / mdbook-sidebar-scrollbox >
< noscript >
< iframe class = "sidebar-iframe-outer" src = "../toc.html" > < / iframe >
< / noscript >
< div id = "mdbook-sidebar-resize-handle" class = "sidebar-resize-handle" >
< div class = "sidebar-resize-indicator" > < / div >
< / div >
< / nav >
< div id = "mdbook-page-wrapper" class = "page-wrapper" >
< div class = "page" >
< div id = "mdbook-menu-bar-hover-placeholder" > < / div >
< div id = "mdbook-menu-bar" class = "menu-bar sticky" >
< div class = "left-buttons" >
< label id = "mdbook-sidebar-toggle" class = "icon-button" for = "mdbook-sidebar-toggle-anchor" title = "Toggle Table of Contents" aria-label = "Toggle Table of Contents" aria-controls = "mdbook-sidebar" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 448 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M0 96C0 78.3 14.3 64 32 64H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32C14.3 128 0 113.7 0 96zM0 256c0-17.7 14.3-32 32-32H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32c-17.7 0-32-14.3-32-32zM448 416c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32s14.3-32 32-32H416c17.7 0 32 14.3 32 32z" / > < / svg > < / span >
< / label >
< button id = "mdbook-theme-toggle" class = "icon-button" type = "button" title = "Change theme" aria-label = "Change theme" aria-haspopup = "true" aria-expanded = "false" aria-controls = "mdbook-theme-list" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 576 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M371.3 367.1c27.3-3.9 51.9-19.4 67.2-42.9L600.2 74.1c12.6-19.5 9.4-45.3-7.6-61.2S549.7-4.4 531.1 9.6L294.4 187.2c-24 18-38.2 46.1-38.4 76.1L371.3 367.1zm-19.6 25.4l-116-104.4C175.9 290.3 128 339.6 128 400c0 3.9 .2 7.8 .6 11.6c1.8 17.5-10.2 36.4-27.8 36.4H96c-17.7 0-32 14.3-32 32s14.3 32 32 32H240c61.9 0 112-50.1 112-112c0-2.5-.1-5-.2-7.5z" / > < / svg > < / span >
< / button >
< ul id = "mdbook-theme-list" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-default_theme" > Auto< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-light" > Light< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-rust" > Rust< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-ayu" > Ayu< / button > < / li >
< / ul >
< button id = "mdbook-search-toggle" class = "icon-button" type = "button" title = "Search (`/`)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "/ s" aria-controls = "mdbook-searchbar" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M416 208c0 45.9-14.9 88.3-40 122.7L502.6 457.4c12.5 12.5 12.5 32.8 0 45.3s-32.8 12.5-45.3 0L330.7 376c-34.4 25.2-76.8 40-122.7 40C93.1 416 0 322.9 0 208S93.1 0 208 0S416 93.1 416 208zM208 352c79.5 0 144-64.5 144-144s-64.5-144-144-144S64 128.5 64 208s64.5 144 144 144z" / > < / svg > < / span >
< / button >
< / div >
< h1 class = "menu-title" > Rust语言圣经(Rust Course)< / h1 >
< div class = "right-buttons" >
< a href = "../print.html" title = "Print this book" aria-label = "Print this book" >
< span class = fa-svg id = "print-button" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M128 0C92.7 0 64 28.7 64 64v96h64V64H354.7L384 93.3V160h64V93.3c0-17-6.7-33.3-18.7-45.3L400 18.7C388 6.7 371.7 0 354.7 0H128zM384 352v32 64H128V384 368 352H384zm64 32h32c17.7 0 32-14.3 32-32V256c0-35.3-28.7-64-64-64H64c-35.3 0-64 28.7-64 64v96c0 17.7 14.3 32 32 32H64v64c0 35.3 28.7 64 64 64H384c35.3 0 64-28.7 64-64V384zm-16-88c-13.3 0-24-10.7-24-24s10.7-24 24-24s24 10.7 24 24s-10.7 24-24 24z" / > < / svg > < / span >
< / a >
< a href = "https://github.com/sunface/rust-course" title = "Git repository" aria-label = "Git repository" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 496 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M165.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6zm-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3zm44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9zM244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8zM97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z" / > < / svg > < / span >
< / a >
< a href = "https://github.com/sunface/rust-course/edit/main/src/first-try/hello-world.md" title = "Suggest an edit" aria-label = "Suggest an edit" rel = "edit" >
< span class = fa-svg id = "git-edit-button" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M421.7 220.3l-11.3 11.3-22.6 22.6-205 205c-6.6 6.6-14.8 11.5-23.8 14.1L30.8 511c-8.4 2.5-17.5 .2-23.7-6.1S-1.5 489.7 1 481.2L38.7 353.1c2.6-9 7.5-17.2 14.1-23.8l205-205 22.6-22.6 11.3-11.3 33.9 33.9 62.1 62.1 33.9 33.9zM96 353.9l-9.3 9.3c-.9 .9-1.6 2.1-2 3.4l-25.3 86 86-25.3c1.3-.4 2.5-1.1 3.4-2l9.3-9.3H112c-8.8 0-16-7.2-16-16V353.9zM453.3 19.3l39.4 39.4c25 25 25 65.5 0 90.5l-14.5 14.5-22.6 22.6-11.3 11.3-33.9-33.9-62.1-62.1L314.3 67.7l11.3-11.3 22.6-22.6 14.5-14.5c25-25 65.5-25 90.5 0z" / > < / svg > < / span >
< / a >
< / div >
< / div >
< div id = "mdbook-search-wrapper" class = "hidden" >
< form id = "mdbook-searchbar-outer" class = "searchbar-outer" >
< div class = "search-wrapper" >
< input type = "search" id = "mdbook-searchbar" name = "searchbar" placeholder = "Search this book ..." aria-controls = "mdbook-searchresults-outer" aria-describedby = "searchresults-header" >
< div class = "spinner-wrapper" >
< span class = fa-svg id = "fa-spin" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M304 48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zm0 416c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM48 304c26.5 0 48-21.5 48-48s-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48zm464-48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM142.9 437c18.7-18.7 18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zm0-294.2c18.7-18.7 18.7-49.1 0-67.9S93.7 56.2 75 75s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zM369.1 437c18.7 18.7 49.1 18.7 67.9 0s18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9z" / > < / svg > < / span >
< / div >
< / div >
< / form >
< div id = "mdbook-searchresults-outer" class = "searchresults-outer hidden" >
< div id = "mdbook-searchresults-header" class = "searchresults-header" > < / div >
< ul id = "mdbook-searchresults" >
< / ul >
< / div >
< / div >
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
< script >
document.getElementById('mdbook-sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('mdbook-sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#mdbook-sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
< / script >
< div id = "mdbook-content" class = "content" >
< main >
< h1 id = "不仅仅是-hello-world" > < a class = "header" href = "#不仅仅是-hello-world" > 不仅仅是 Hello world< / a > < / h1 >
< p > 几乎所有教程中安装的最后一个环节都是 < code > hello world< / code > ，我们也不能免俗。但是，在 < code > hello world< / code > 之后， ， ， < / p >
< h2 id = "多国语言的世界你好" > < a class = "header" href = "#多国语言的世界你好" > 多国语言的“世界，你好“< / a > < / h2 >
< p > 还记得大明湖畔等你的 < a href = "https://course.rs/first-try/editor.html" > VSCode IDE< / a > 和通过 < code > Cargo< / code > 创建的 < a href = "https://course.rs/first-try/cargo.html" > 世界，你好< / a > 工程吗？< / p >
< p > 现在使用 VSCode 打开 < a href = "https://course.rs/first-try/cargo.html" > 上一节< / a > 中创建的 < code > world_hello< / code > 工程，然后进入 < code > main.rs< / code > 文件。（此文件是当前 Rust 工程的入口文件，和其它语言几无区别。）< / p >
< p > 接下来，对世界友人给予热切的问候：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn greet_world() {
let southern_germany = "Grüß Gott!";
let chinese = "世界，你好";
let english = "World, hello";
let regions = [southern_germany, chinese, english];
for region in regions.iter() {
println!("{}", & region);
}
}
fn main() {
greet_world();
}< / code > < / pre >
< p > 打开终端，进入 < code > world_hello< / code > 工程根目录，运行该程序。（你也可以在 VSCode 中打开终端，方法是点击 VSCode 上方菜单栏中的终端-> 新建终端，或者直接使用快捷键打开。）< / p >
< pre > < code class = "language-console" > $ cargo run
Compiling world_hello v0.1.0 (/Users/sunfei/development/rust/world_hello)
Finished dev [unoptimized + debuginfo] target(s) in 0.21s
Running `target/debug/world_hello`
Grüß Gott!
世界，你好
World, hello
< / code > < / pre >
< p > 你的热情，就像一把火，燃烧了整个世界~ 花点时间来看看上面的代码：< / p >
< p > 首先， < / p >
< p > 其次，关注下 < code > println< / code > 后面的 < code > !< / code > ，如果你有 Ruby 编程经验，那么你可能会认为这是解构操作符，但是在 Rust 中，这是 < code > 宏< / code > 操作符，你目前可以认为宏是一种特殊类型函数。< / p >
< p > 对于 < code > println< / code > 来说，我们没有使用其它语言惯用的 < code > %s< / code > 、< code > %d< / code > 来做输出占位符，而是使用 < code > {}< / code > ，因为 Rust 在底层帮我们做了大量工作，会自动识别输出数据的类型，例如当前例子，会识别为 < code > & str< / code > 类型。< / p >
< p > 最后， ， < code > .iter()< / code > 方法），才能用于迭代循环。在目前来看，你会觉得这一点好像挺麻烦，不急，以后就知道这么做的好处所在。< / p >
< blockquote >
< p > 实际上这段代码可以简写，在 2021 edition 及以后，支持直接写 < code > for region in regions< / code > ，原因会在迭代器章节的开头提到，是因为 for 隐式地将 regions 转换成迭代器。< / p >
< / blockquote >
< p > 至于函数声明、调用、数组的使用， ， ！ < / p >
< h2 id = "rust-语言初印象" > < a class = "header" href = "#rust-语言初印象" > Rust 语言初印象< / a > < / h2 >
< p > Haskell 和 Java 开发者们可能会觉得Rust 这门语言很熟悉， ， ， < / p >
< p > 上面的 < code > So Easy< / code > 的余音仍在绕梁，我希望它能继续下去，可是… 人总是要面对现实，因此让我们来点狠活：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let penguin_data = "\
common name,length (cm)
Little penguin,33
Yellow-eyed penguin,65
Fiordland penguin,60
Invalid,data
";
let records = penguin_data.lines();
for (i, record) in records.enumerate() {
if i == 0 || record.trim().len() == 0 {
continue;
}
// 声明一个 fields 变量，类型是 Vec
// Vec 是 vector 的缩写，是一个可伸缩的集合类型，可以认为是一个动态数组
// < _> 表示 Vec 中的元素类型由编译器自行推断，在很多场景下，都会帮我们省却不少功夫
let fields: Vec< _> = record
.split(',')
.map(|field| field.trim())
.collect();
if cfg!(debug_assertions) {
// 输出到标准错误输出
eprintln!("debug: {:?} -> {:?}",
record, fields);
}
let name = fields[0];
// 1. 尝试把 fields[1] 的值转换为 f32 类型的浮点数，如果成功，则把 f32 值赋给 length 变量
//
// 2. if let 是一个匹配表达式，用来从=右边的结果中，匹配出 length 的值：
// 1） ，
// 2）
//
// 3. 当然你也可以忽略成功的情况，用 if let Err(e) = fields[1].parse::< f32> () {...}匹配出错误，然后打印出来，但是没啥卵用
if let Ok(length) = fields[1].parse::< f32> () {
// 输出到标准输出
println!("{}, {}cm", name, length);
}
}
}< / code > < / pre >
< p > 看完这段代码，不知道你的余音有没有戛然而止，反正我已经在颤抖了。这就是传说中的下马威吗？😵< / p >
< p > 上面代码中，值得注意的 Rust 特性有：< / p >
< ul >
< li > 控制流：< code > for< / code > 和 < code > continue< / code > 连在一起使用，实现循环控制。< / li >
< li > 方法语法：由于 Rust 没有继承，因此 Rust 不是传统意义上的面向对象语言，但是它却从 < code > OO< / code > 语言那里偷师了方法的使用 < code > record.trim()< / code > ， < code > record.split(',')< / code > 等。< / li >
< li > 高阶函数编程：函数可以作为参数也能作为返回值，例如 < code > .map(|field| field.trim())< / code > ，这里 < code > map< / code > 方法中使用闭包函数作为参数，也可以称呼为 < code > 匿名函数< / code > 、< code > lambda 函数< / code > 。< / li >
< li > 类型标注：< code > if let Ok(length) = fields[1].parse::< f32> ()< / code > ，通过 < code > ::< f32> < / code > 的使用，告诉编译器 < code > length< / code > 是一个 < code > f32< / code > 类型的浮点数。这种类型标注不是很常用，但是在编译器无法推断出你的数据类型时，就很有用了。< / li >
< li > 条件编译：< code > if cfg!(debug_assertions)< / code > ，说明紧跟其后的输出（打印）只在 < code > debug< / code > 模式下生效。< / li >
< li > 隐式返回： < code > return< / code > 关键字用于函数返回，但是在很多时候，我们可以省略它。因为 Rust 是 < a href = "https://course.rs/basic/base-type/statement-expression.html" > < strong > 基于表达式的语言< / strong > < / a > 。< / li >
< / ul >
< p > 在终端中运行上述代码时，会看到很多 < code > debug: ...< / code > 的输出，上面有讲，这些都是 < code > 条件编译< / code > 的输出，那么该怎么消除掉这些输出呢？< / p >
< p > 读者大大普遍冰雪聪明，肯定已经想到：是的，在 < a href = "https://course.rs/first-try/cargo.html#手动编译和运行项目" > 认识 Cargo< / a > 中，曾经介绍过 < code > --release< / code > 参数，因为 < code > cargo run< / code > 默认是运行 < code > debug< / code > 模式。因此想要消灭那些 < code > debug:< / code > 输出，需要更改为其它模式，其中最常用的模式就是 < code > --release< / code > 也就是生产发布的模式。< / p >
< p > 具体运行代码就不给了，留给大家作为一个小练习，建议亲自动手尝试下。< / p >
< p > 至此， < strong > 这本书就像优秀的国外课本一样，不太枯燥。也希望这本不太枯燥的书，能伴你长行，犹如一杯奶茶，细细品之，唇齿留香。< / strong > < / p >
< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "../first-try/cargo.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z" / > < / svg > < / span >
< / a >
< a rel = "next prefetch" href = "../first-try/slowly-downloading.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z" / > < / svg > < / span >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
< a rel = "prev" href = "../first-try/cargo.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z" / > < / svg > < / span >
< / a >
< a rel = "next prefetch" href = "../first-try/slowly-downloading.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z" / > < / svg > < / span >
< / a >
< / nav >
< / div >
< template id = fa-eye > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 576 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z" / > < / svg > < / span > < / template >
< template id = fa-eye-slash > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 640 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M38.8 5.1C28.4-3.1 13.3-1.2 5.1 9.2S-1.2 34.7 9.2 42.9l592 464c10.4 8.2 25.5 6.3 33.7-4.1s6.3-25.5-4.1-33.7L525.6 386.7c39.6-40.6 66.4-86.1 79.9-118.4c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C465.5 68.8 400.8 32 320 32c-68.2 0-125 26.3-169.3 60.8L38.8 5.1zM223.1 149.5C248.6 126.2 282.7 112 320 112c79.5 0 144 64.5 144 144c0 24.9-6.3 48.3-17.4 68.7L408 294.5c5.2-11.8 8-24.8 8-38.5c0-53-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6c0 10.2-2.4 19.8-6.6 28.3l-90.3-70.8zm223.1 298L373 389.9c-16.4 6.5-34.3 10.1-53 10.1c-79.5 0-144-64.5-144-144c0-6.9 .5-13.6 1.4-20.2L83.1 161.5C60.3 191.2 44 220.8 34.5 243.7c-3.3 7.9-3.3 16.7 0 24.6c14.9 35.7 46.2 87.7 93 131.1C174.5 443.2 239.2 480 320 480c47.8 0 89.9-12.9 126.2-32.5z" / > < / svg > < / span > < / template >
< template id = fa-copy > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M502.6 70.63l-61.25-61.25C435.4 3.371 427.2 0 418.7 0H255.1c-35.35 0-64 28.66-64 64l.0195 256C192 355.4 220.7 384 256 384h192c35.2 0 64-28.8 64-64V93.25C512 84.77 508.6 76.63 502.6 70.63zM464 320c0 8.836-7.164 16-16 16H255.1c-8.838 0-16-7.164-16-16L239.1 64.13c0-8.836 7.164-16 16-16h128L384 96c0 17.67 14.33 32 32 32h47.1V320zM272 448c0 8.836-7.164 16-16 16H63.1c-8.838 0-16-7.164-16-16L47.98 192.1c0-8.836 7.164-16 16-16H160V128H63.99c-35.35 0-64 28.65-64 64l.0098 256C.002 483.3 28.66 512 64 512h192c35.2 0 64-28.8 64-64v-32h-47.1L272 448z" / > < / svg > < / span > < / template >
< template id = fa-play > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 384 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M73 39c-14.8-9.1-33.4-9.4-48.5-.9S0 62.6 0 80V432c0 17.4 9.4 33.4 24.5 41.9s33.7 8.1 48.5-.9L361 297c14.3-8.7 23-24.2 23-41s-8.7-32.2-23-41L73 39z" / > < / svg > < / span > < / template >
< template id = fa-clock-rotate-left > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M75 75L41 41C25.9 25.9 0 36.6 0 57.9V168c0 13.3 10.7 24 24 24H134.1c21.4 0 32.1-25.9 17-41l-30.8-30.8C155 85.5 203 64 256 64c106 0 192 86 192 192s-86 192-192 192c-40.8 0-78.6-12.7-109.7-34.4c-14.5-10.1-34.4-6.6-44.6 7.9s-6.6 34.4 7.9 44.6C151.2 495 201.7 512 256 512c141.4 0 256-114.6 256-256S397.4 0 256 0C185.3 0 121.3 28.7 75 75zm181 53c-13.3 0-24 10.7-24 24V256c0 6.4 2.5 12.5 7 17l72 72c9.4 9.4 24.6 9.4 33.9 0s9.4-24.6 0-33.9l-65-65V152c0-13.3-10.7-24-24-24z" / > < / svg > < / span > < / template >
< script >
window.playground_copyable = true;
< / script >
< script src = "../ace-2a3cd908.js" > < / script >
< script src = "../mode-rust-2c9d5c9a.js" > < / script >
< script src = "../editor-16ca416c.js" > < / script >
< script src = "../theme-dawn-4493f9c8.js" > < / script >
< script src = "../theme-tomorrow_night-9dbe62a9.js" > < / script >
< script src = "../elasticlunr-ef4e11c1.min.js" > < / script >
< script src = "../mark-09e88c2c.min.js" > < / script >
< script src = "../searcher-c2a407aa.js" > < / script >
< script src = "../clipboard-1626706a.min.js" > < / script >
< script src = "../highlight-abc7f01d.js" > < / script >
< script src = "../book-a0b12cfe.js" > < / script >
<!-- Custom JS scripts -->
< script src = "../assets/custom-690c9de5.js" > < / script >
< script src = "../assets/bigPicture-be03f9c8.js" > < / script >
< / div >
< / body >
< / html >
