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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="Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/hashbrown-0.11.2/src/macros.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>macros.rs - source</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="../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled ><script id="default-settings"></script><script src="../../storage.js"></script><script src="../../crates.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../favicon.svg">
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</pre><div class="example-wrap"><pre class="rust ">
<span class="comment">// See the cfg-if crate.</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">cfg_if</span> {
<span class="comment">// match if/else chains with a final `else`</span>
($(
<span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">meta</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>)]</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>:<span class="ident">item</span>)<span class="op">*</span> }
) <span class="kw">else</span> <span class="op">*</span> <span class="kw">else</span> {
$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it2</span>:<span class="ident">item</span>)<span class="op">*</span>
}) <span class="op">=</span><span class="op">></span> {
<span class="macro">cfg_if</span><span class="macro">!</span> {
@<span class="ident">__items</span>
() ;
$( ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">meta</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>)<span class="kw-2">*</span>) ), )<span class="op">*</span>
( () ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it2</span>)<span class="kw-2">*</span>) ),
}
};
<span class="comment">// match if/else chains lacking a final `else`</span>
(
<span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_met</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>)]</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_it</span>:<span class="ident">item</span>)<span class="op">*</span> }
$(
<span class="kw">else</span> <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_met</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>)]</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_it</span>:<span class="ident">item</span>)<span class="op">*</span> }
)<span class="op">*</span>
) <span class="op">=</span><span class="op">></span> {
<span class="macro">cfg_if</span><span class="macro">!</span> {
@<span class="ident">__items</span>
() ;
( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_met</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_it</span>)<span class="kw-2">*</span>) ),
$( ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_met</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_it</span>)<span class="kw-2">*</span>) ), )<span class="op">*</span>
( () () ),
}
};
<span class="comment">// Internal and recursive macro to emit all the items</span>
<span class="comment">//</span>
<span class="comment">// Collects all the negated cfgs in a list at the beginning and after the</span>
<span class="comment">// semicolon is all the remaining items</span>
(@<span class="ident">__items</span> ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>:<span class="ident">meta</span>,)<span class="kw-2">*</span>) ; ) <span class="op">=</span><span class="op">></span> {};
(@<span class="ident">__items</span> ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>:<span class="ident">meta</span>,)<span class="kw-2">*</span>) ; ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>:<span class="ident">item</span>)<span class="kw-2">*</span>) ), $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
<span class="comment">// Emit all items within one block, applying an approprate #[cfg]. The</span>
<span class="comment">// #[cfg] will require all `$m` matchers specified and must also negate</span>
<span class="comment">// all previous matchers.</span>
<span class="macro">cfg_if</span><span class="macro">!</span> { @<span class="ident">__apply</span> <span class="ident">cfg</span>(<span class="ident">all</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>,)<span class="op">*</span> <span class="ident">not</span>(<span class="ident">any</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>),<span class="kw-2">*</span>)))), $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>)<span class="op">*</span> }
<span class="comment">// Recurse to emit all other items in `$rest`, and when we do so add all</span>
<span class="comment">// our `$m` matchers to the list of `$not` matchers as future emissions</span>
<span class="comment">// will have to negate everything we just matched as well.</span>
<span class="macro">cfg_if</span><span class="macro">!</span> { @<span class="ident">__items</span> ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>,)<span class="op">*</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>,)<span class="kw-2">*</span>) ; $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span>)<span class="op">*</span> }
};
<span class="comment">// Internal macro to Apply a cfg attribute to a list of items</span>
(@<span class="ident">__apply</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>:<span class="ident">meta</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>:<span class="ident">item</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
$(<span class="attribute">#[<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>]</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>)<span class="op">*</span>
};
}
<span class="comment">// Helper macro for specialization. This also helps avoid parse errors if the</span>
<span class="comment">// default fn syntax for specialization changes in the future.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"nightly"</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">default_fn</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tt</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
<span class="ident">default</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tt</span>)<span class="op">*</span>
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"nightly"</span>))]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">default_fn</span> {
($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tt</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> {
$(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tt</span>)<span class="op">*</span>
}
}
</pre></div>
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