<!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="Source to the Rust file `src/liballoc/macros.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>macros.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../normalize1.35.0.css"><link rel="stylesheet" type="text/css" href="../../rustdoc1.35.0.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark1.35.0.css"><link rel="stylesheet" type="text/css" href="../../light1.35.0.css" id="themeStyle"><script src="../../storage1.35.0.js"></script><noscript><link rel="stylesheet" href="../../noscript1.35.0.css"></noscript><link rel="shortcut icon" href="../../favicon1.35.0.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow1.35.0.svg");}</style></head><body class="rustdoc source"><!--[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='../../alloc/index.html'><img src='../../rust-logo1.35.0.png' alt='logo' width='100'></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush1.35.0.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme1.35.0.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="../../wheel1.35.0.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><div class="example-wrap"><pre class="rust ">
<span class="doccomment">/// Creates a [`Vec`] containing the arguments.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `vec!` allows `Vec`s to be defined with the same syntax as array expressions.</span>
<span class="doccomment">/// There are two forms of this macro:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - Create a [`Vec`] containing a given list of elements:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let v = vec![1, 2, 3];</span>
<span class="doccomment">/// assert_eq!(v[0], 1);</span>
<span class="doccomment">/// assert_eq!(v[1], 2);</span>
<span class="doccomment">/// assert_eq!(v[2], 3);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - Create a [`Vec`] from a given element and size:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let v = vec![1; 3];</span>
<span class="doccomment">/// assert_eq!(v, [1, 1, 1]);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that unlike array expressions this syntax supports all elements</span>
<span class="doccomment">/// which implement [`Clone`] and the number of elements doesn't have to be</span>
<span class="doccomment">/// a constant.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This will use `clone` to duplicate an expression, so one should be careful</span>
<span class="doccomment">/// using this with types having a nonstandard `Clone` implementation. For</span>
<span class="doccomment">/// example, `vec![Rc::new(1); 5]` will create a vector of five references</span>
<span class="doccomment">/// to the same boxed integer value, not five references pointing to independently</span>
<span class="doccomment">/// boxed integers.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Vec`]: ../std/vec/struct.Vec.html</span>
<span class="doccomment">/// [`Clone`]: ../std/clone/trait.Clone.html</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">test</span>))]</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="attribute">#[<span class="ident">allow_internal_unstable</span>(<span class="ident">box_syntax</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">vec</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">elem</span>:<span class="ident">expr</span>; <span class="macro-nonterminal">$</span><span class="macro-nonterminal">n</span>:<span class="ident">expr</span>) <span class="op">=></span> (
<span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro-nonterminal">vec</span>::<span class="ident">from_elem</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">elem</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">n</span>)
);
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>:<span class="ident">expr</span>),<span class="kw-2">*</span>) <span class="op">=></span> (
<span class="op"><</span>[<span class="kw">_</span>]<span class="op">></span>::<span class="ident">into_vec</span>(<span class="kw">box</span> [$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>),<span class="kw-2">*</span>])
);
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>:<span class="ident">expr</span>,)<span class="kw-2">*</span>) <span class="op">=></span> (<span class="macro">vec</span><span class="macro">!</span>[$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>),<span class="kw-2">*</span>])
}
<span class="comment">// HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is</span>
<span class="comment">// required for this macro definition, is not available. Instead use the</span>
<span class="comment">// `slice::into_vec` function which is only available with cfg(test)</span>
<span class="comment">// NB see the slice::hack module in slice.rs for more information</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">vec</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">elem</span>:<span class="ident">expr</span>; <span class="macro-nonterminal">$</span><span class="macro-nonterminal">n</span>:<span class="ident">expr</span>) <span class="op">=></span> (
<span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro-nonterminal">vec</span>::<span class="ident">from_elem</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">elem</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">n</span>)
);
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>:<span class="ident">expr</span>),<span class="kw-2">*</span>) <span class="op">=></span> (
<span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro-nonterminal">slice</span>::<span class="ident">into_vec</span>(<span class="kw">box</span> [$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>),<span class="kw-2">*</span>])
);
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>:<span class="ident">expr</span>,)<span class="kw-2">*</span>) <span class="op">=></span> (<span class="macro">vec</span><span class="macro">!</span>[$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>),<span class="kw-2">*</span>])
}
<span class="doccomment">/// Creates a `String` using interpolation of runtime expressions.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The first argument `format!` receives is a format string. This must be a string</span>
<span class="doccomment">/// literal. The power of the formatting string is in the `{}`s contained.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Additional parameters passed to `format!` replace the `{}`s within the</span>
<span class="doccomment">/// formatting string in the order given unless named or positional parameters</span>
<span class="doccomment">/// are used; see [`std::fmt`][fmt] for more information.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A common use for `format!` is concatenation and interpolation of strings.</span>
<span class="doccomment">/// The same convention is used with [`print!`] and [`write!`] macros,</span>
<span class="doccomment">/// depending on the intended destination of the string.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// To convert a single value to a string, use the [`to_string`] method. This</span>
<span class="doccomment">/// will use the [`Display`] formatting trait.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [fmt]: ../std/fmt/index.html</span>
<span class="doccomment">/// [`print!`]: ../std/macro.print.html</span>
<span class="doccomment">/// [`write!`]: ../std/macro.write.html</span>
<span class="doccomment">/// [`to_string`]: ../std/string/trait.ToString.html</span>
<span class="doccomment">/// [`Display`]: ../std/fmt/trait.Display.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `format!` panics if a formatting trait implementation returns an error.</span>
<span class="doccomment">/// This indicates an incorrect implementation</span>
<span class="doccomment">/// since `fmt::Write for String` never returns an error itself.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// format!("test");</span>
<span class="doccomment">/// format!("hello {}", "world!");</span>
<span class="doccomment">/// format!("x = {}, y = {y}", 10, y = 30);</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">format</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=></span> (<span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro-nonterminal">fmt</span>::<span class="ident">format</span>(<span class="macro">format_args</span><span class="macro">!</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>)<span class="kw-2">*</span>)))
}
</pre></div>
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