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<meta name="description" content="API documentation for the Rust `bail` macro in crate `error_chain`.">
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<title>error_chain::bail - Rust</title>
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<h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>error_chain</a>::<wbr><a class="macro" href=''>bail</a></span><span class='out-of-band'><span id='render-detail'>
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<pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">bail</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>) <span class="op">=&gt;</span> { ... };
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>:<span class="ident">tt</span>)<span class="op">+</span>) <span class="op">=&gt;</span> { ... };
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}</pre>
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<div class='docblock'><p>Exits a function early with an error</p>
<p>The <code>bail!</code> macro provides an easy way to exit a function.
<code>bail!(expr)</code> is equivalent to writing.</p>
<pre class="rust rust-example-rendered">
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">expr</span>.<span class="ident">into</span>());</pre>
<p>And as shorthand it takes a formatting string a la <code>println!</code>:</p>
<pre class="rust rust-example-rendered">
<span class="macro">bail</span><span class="macro">!</span>(<span class="string">&quot;bad number: {}&quot;</span>, <span class="ident">n</span>);</pre>
<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
<p>Bailing on a custom error:</p>
<pre class="rust rust-example-rendered">
<span class="macro">error_chain</span><span class="macro">!</span> {
<span class="ident">errors</span> { <span class="ident">FooError</span> }
}
<span class="kw">fn</span> <span class="ident">foo</span>() <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span>()<span class="op">&gt;</span> {
<span class="kw">if</span> <span class="ident">bad_condition</span>() {
<span class="macro">bail</span><span class="macro">!</span>(<span class="ident">ErrorKind</span>::<span class="ident">FooError</span>);
}
<span class="prelude-val">Ok</span>(())
}
</pre>
<p>Bailing on a formatted string:</p>
<pre class="rust rust-example-rendered">
<span class="macro">error_chain</span><span class="macro">!</span> { }
<span class="kw">fn</span> <span class="ident">foo</span>() <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span>()<span class="op">&gt;</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">bad_num</span>) <span class="op">=</span> <span class="ident">bad_condition</span>() {
<span class="macro">bail</span><span class="macro">!</span>(<span class="string">&quot;so bad: {}&quot;</span>, <span class="ident">bad_num</span>);
}
<span class="prelude-val">Ok</span>(())
}
</pre>
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