rust
/
rust-course
mirror of https://github.com/sunface/rust-course
5
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
Branches Tags
${ item.name }
Create tag ${ searchTerm }
Create branch ${ searchTerm }
from 'gh-pages'
${ noResults }
rust-course/basic-practice/envs.html

389 lines
18 KiB
Raw Permalink Normal View History Unescape

deploy
1 week ago
<!DOCTYPE HTML>
<html lang="zh-CN" class="light sidebar-visible" dir="ltr">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>使用环境变量 - 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.svg">
<link rel="shortcut icon" href="../favicon.png">
<link rel="stylesheet" href="../css/variables.css">
<link rel="stylesheet" href="../css/general.css">
<link rel="stylesheet" href="../css/chrome.css">
<link rel="stylesheet" href="../css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="../fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" id="highlight-css" href="../highlight.css">
<link rel="stylesheet" id="tomorrow-night-css" href="../tomorrow-night.css">
<link rel="stylesheet" id="ayu-highlight-css" href="../ayu-highlight.css">
<!-- Custom theme stylesheets -->
<link rel="stylesheet" href="../theme/style.css">
<!-- Provide site root and default themes to javascript -->
<script>
const path_to_root = "../";
const default_light_theme = "light";
const default_dark_theme = "navy";
</script>
<!-- Start loading toc.js asap -->
<script src="../toc.js"></script>
</head>
<body>
<div id="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="sidebar-toggle-anchor" class="hidden">
<!-- Hide / unhide sidebar before it is displayed -->
<script>
let sidebar = null;
const sidebar_toggle = document.getElementById("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 = sidebar === 'visible';
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
</script>
<nav id="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="sidebar-resize-handle" class="sidebar-resize-handle">
<div class="sidebar-resize-indicator"></div>
</div>
</nav>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky">
<div class="left-buttons">
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</label>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li>
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
<i class="fa fa-search"></i>
</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">
<i id="print-button" class="fa fa-print"></i>
</a>
<a href="https://github.com/sunface/rust-course" title="Git repository" aria-label="Git repository">
<i id="git-repository-button" class="fa fa-github"></i>
</a>
<a href="https://github.com/sunface/rust-course/edit/main/src/basic-practice/envs.md" title="Suggest an edit" aria-label="Suggest an edit">
<i id="git-edit-button" class="fa fa-edit"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script>
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<main>
<h1 id="使用环境变量来增强程序"><a class="header" href="#使用环境变量来增强程序">使用环境变量来增强程序</a></h1>
<p>在上一章节中，留下了一个悬念，该如何实现用户控制的大小写敏感，其实答案很简单，你在其它程序中肯定也遇到过不少，例如如何控制 <code>panic</code> 后的栈展开？ Rust 提供的解决方案是通过命令行参数来控制:</p>
<pre><code class="language-shell">RUST_BACKTRACE=1 cargo run
</code></pre>
<p>与之类似，我们也可以使用环境变量来控制大小写敏感，例如:</p>
<pre><code class="language-shell">IGNORE_CASE=1 cargo run -- to poem.txt
</code></pre>
<p>既然有了目标，那么一起来看看该如何实现吧。</p>
<h2 id="编写大小写不敏感的测试用例"><a class="header" href="#编写大小写不敏感的测试用例">编写大小写不敏感的测试用例</a></h2>
<p>还是遵循之前的规则：测试驱动，这次是对一个新的大小写不敏感函数进行测试 <code>search_case_insensitive</code>。</p>
<p>还记得 TDD 的测试步骤嘛？首先编写一个注定失败的用例:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in src/lib.rs
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn case_sensitive() {
let query = "duct";
let contents = "\
Rust:
safe, fast, productive.
Pick three.
Duct tape.";
assert_eq!(vec!["safe, fast, productive."], search(query, contents));
}
#[test]
fn case_insensitive() {
let query = "rUsT";
let contents = "\
Rust:
safe, fast, productive.
Pick three.
Trust me.";
assert_eq!(
vec!["Rust:", "Trust me."],
search_case_insensitive(query, contents)
);
}
}
<span class="boring">}</span></code></pre></pre>
<p>可以看到，这里新增了一个 <code>case_insensitive</code> 测试用例，并对 <code>search_case_insensitive</code> 进行了测试，结果显而易见，函数都没有实现，自然会失败。</p>
<p>接着来实现这个大小写不敏感的搜索函数:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub fn search_case_insensitive&lt;'a&gt;(
query: &amp;str,
contents: &amp;'a str,
) -&gt; Vec&lt;&amp;'a str&gt; {
let query = query.to_lowercase();
let mut results = Vec::new();
for line in contents.lines() {
if line.to_lowercase().contains(&amp;query) {
results.push(line);
}
}
results
}
<span class="boring">}</span></code></pre></pre>
<p>跟之前一样，但是引入了一个新的方法 <code>to_lowercase</code>，它会将 <code>line</code> 转换成全小写的字符串，类似的方法在其它语言中也差不多，就不再赘述。</p>
<p>还要注意的是 <code>query</code> 现在是 <code>String</code> 类型，而不是之前的 <code>&amp;str</code>，因为 <code>to_lowercase</code> 返回的是 <code>String</code>。</p>
<p>修改后，再来跑一次测试，看能否通过。</p>
<pre><code class="language-shell">$ cargo test
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished test [unoptimized + debuginfo] target(s) in 1.33s
Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
running 2 tests
test tests::case_insensitive ... ok
test tests::case_sensitive ... ok
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Running unittests src/main.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Doc-tests minigrep
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
</code></pre>
<p>Ok，TDD的第二步也完成了，测试通过，接下来就是最后一步，在 <code>run</code> 中调用新的搜索函数。但是在此之前，要新增一个配置项，用于控制是否开启大小写敏感。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in lib.rs
pub struct Config {
pub query: String,
pub file_path: String,
pub ignore_case: bool,
}
<span class="boring">}</span></code></pre></pre>
<p>接下来就是检查该字段，来判断是否启动大小写敏感：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub fn run(config: Config) -&gt; Result&lt;(), Box&lt;dyn Error&gt;&gt; {
let contents = fs::read_to_string(config.file_path)?;
let results = if config.ignore_case {
search_case_insensitive(&amp;config.query, &amp;contents)
} else {
search(&amp;config.query, &amp;contents)
};
for line in results {
println!("{line}");
}
Ok(())
}
<span class="boring">}</span></code></pre></pre>
<p>现在的问题来了，该如何控制这个配置项呢。这个就要借助于章节开头提到的环境变量，好在 Rust 的 <code>env</code> 包提供了相应的方法。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::env;
// --snip--
impl Config {
pub fn build(args: &amp;[String]) -&gt; Result&lt;Config, &amp;'static str&gt; {
if args.len() &lt; 3 {
return Err("not enough arguments");
}
let query = args[1].clone();
let file_path = args[2].clone();
let ignore_case = env::var("IGNORE_CASE").is_ok();
Ok(Config {
query,
file_path,
ignore_case,
})
}
}
<span class="boring">}</span></code></pre></pre>
<p><code>env::var</code> 没啥好说的，倒是 <code>is_ok</code> 值得说道下。该方法是 <code>Result</code> 提供的，用于检查是否有值，有就返回 <code>true</code>，没有则返回 <code>false</code>，刚好完美符合我们的使用场景，因为我们并不关心 <code>Ok&lt;T&gt;</code> 中具体的值。</p>
<p>运行下试试：</p>
<pre><code class="language-shell">$ cargo run -- to poem.txt
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished dev [unoptimized + debuginfo] target(s) in 0.0s
Running `target/debug/minigrep to poem.txt`
Are you nobody, too?
How dreary to be somebody!
</code></pre>
<p>看起来没有问题，接下来测试下大小写不敏感:</p>
<pre><code class="language-shell">$ IGNORE_CASE=1 cargo run -- to poem.txt
</code></pre>
<pre><code class="language-shell">Are you nobody, too?
How dreary to be somebody!
To tell your name the livelong day
To an admiring bog!
</code></pre>
<p>大小写不敏感后，查询到的内容明显多了很多，也很符合我们的预期。</p>
<p>最后，给大家留一个小作业：同时使用命令行参数和环境变量的方式来控制大小写不敏感，其中环境变量的优先级更高，也就是两个都设置的情况下，优先使用环境变量的设置。</p>
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="../basic-practice/tests.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="../basic-practice/stderr.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="../basic-practice/tests.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="../basic-practice/stderr.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script>
window.playground_copyable = true;
</script>
<script src="../ace.js"></script>
<script src="../editor.js"></script>
<script src="../mode-rust.js"></script>
<script src="../theme-dawn.js"></script>
<script src="../theme-tomorrow_night.js"></script>
<script src="../elasticlunr.min.js"></script>
<script src="../mark.min.js"></script>
<script src="../searcher.js"></script>
<script src="../clipboard.min.js"></script>
<script src="../highlight.js"></script>
<script src="../book.js"></script>
<!-- Custom JS scripts -->
<script src="../assets/custom2.js"></script>
<script src="../assets/bigPicture.js"></script>
</div>
</body>
</html>