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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `value_t` macro in crate `clap`."><meta name="keywords" content="rust, rustlang, rust-lang, value_t"><title>clap::value_t - Rust</title><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc macro"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../clap/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class='location'><a href='index.html'>clap</a></p><script>window.sidebarCurrent = {name: 'value_t', ty: 'macro', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/clap/macros.rs.html#61-77' title='goto source code'>[src]</a></span><span class='in-band'>Macro <a href='index.html'>clap</a>::<wbr><a class="macro" href=''>value_t</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">value_t</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>:<span class="ident">ident</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">v</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">ty</span>) <span class="op">=</span><span class="op">></span> { ... };
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>:<span class="ident">ident</span>.<span class="ident">value_of</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">v</span>:<span class="ident">expr</span>), <span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">ty</span>) <span class="op">=</span><span class="op">></span> { ... };
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}</pre></div>
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</div><div class='docblock'><p>Convenience macro getting a typed value <code>T</code> where <code>T</code> implements <a href="https://doc.rust-lang.org/std/str/trait.FromStr.html"><code>std::str::FromStr</code></a> from an
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argument value. This macro returns a <code>Result<T,String></code> which allows you as the developer to
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decide what you'd like to do on a failed parse. There are two types of errors, parse failures
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and those where the argument wasn't present (such as a non-required argument). You can use
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it to get a single value, or a iterator as with the <a href="./struct.ArgMatches.html#method.values_of"><code>ArgMatches::values_of</code></a></p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="ident">matches</span> <span class="op">=</span> <span class="ident">App</span>::<span class="ident">new</span>(<span class="string">"myapp"</span>)
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.<span class="ident">arg_from_usage</span>(<span class="string">"[length] 'Set the length to use as a pos whole num, i.e. 20'"</span>)
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.<span class="ident">get_matches</span>();
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<span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="macro">value_t</span><span class="macro">!</span>(<span class="ident">matches</span>.<span class="ident">value_of</span>(<span class="string">"length"</span>), <span class="ident">u32</span>).<span class="ident">unwrap_or_else</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">exit</span>());
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<span class="kw">let</span> <span class="ident">also_len</span> <span class="op">=</span> <span class="macro">value_t</span><span class="macro">!</span>(<span class="ident">matches</span>, <span class="string">"length"</span>, <span class="ident">u32</span>).<span class="ident">unwrap_or_else</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="ident">e</span>.<span class="ident">exit</span>());
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{} + 2: {}"</span>, <span class="ident">len</span>, <span class="ident">len</span> <span class="op">+</span> <span class="number">2</span>);</pre></div>
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