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<h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>std</a>::<wbr><a class="macro" href=''>unimplemented</a></span><span class='out-of-band'><span id='render-detail'>
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<pre class="rust macro">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">unimplemented</span> {
( ) <span class="op">=></span> { ... };
( $ ( $ <span class="ident">arg</span> : <span class="ident">tt</span> ) <span class="op">+</span> ) <span class="op">=></span> { ... };
}</pre>
<div class='docblock'><p>A standardized placeholder for marking unfinished code.</p>
<p>This can be useful if you are prototyping and are just looking to have your
code typecheck, or if you're implementing a trait that requires multiple
methods, and you're only planning on using one of them.</p>
<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
<p>This will always <a href="macro.panic.html">panic!</a></p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Here's an example of some in-progress code. We have a trait <code>Foo</code>:</p>
<pre class="rust rust-example-rendered">
<span class="kw">trait</span> <span class="ident">Foo</span> {
<span class="kw">fn</span> <span class="ident">bar</span>(<span class="kw-2">&</span><span class="self">self</span>);
<span class="kw">fn</span> <span class="ident">baz</span>(<span class="kw-2">&</span><span class="self">self</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Atrait%20Foo%20%7B%0A%20%20%20%20fn%20bar(%26self)%3B%0A%20%20%20%20fn%20baz(%26self)%3B%0A%7D%0A%7D">Run</a></pre>
<p>We want to implement <code>Foo</code> on one of our types, but we also want to work on
just <code>bar()</code> first. In order for our code to compile, we need to implement
<code>baz()</code>, so we can use <code>unimplemented!</code>:</p>
<pre class="rust rust-example-rendered">
<span class="kw">struct</span> <span class="ident">MyStruct</span>;
<span class="kw">impl</span> <span class="ident">Foo</span> <span class="kw">for</span> <span class="ident">MyStruct</span> {
<span class="kw">fn</span> <span class="ident">bar</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// implementation goes here</span>
}
<span class="kw">fn</span> <span class="ident">baz</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// let's not worry about implementing baz() for now</span>
<span class="macro">unimplemented</span><span class="macro">!</span>();
}
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">MyStruct</span>;
<span class="ident">s</span>.<span class="ident">bar</span>();
<span class="comment">// we aren't even using baz() yet, so this is fine.</span>
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Atrait%20Foo%20%7B%0A%20%20%20%20fn%20bar(%26self)%3B%0A%20%20%20%20fn%20baz(%26self)%3B%0A%7D%0Astruct%20MyStruct%3B%0A%0Aimpl%20Foo%20for%20MyStruct%20%7B%0A%20%20%20%20fn%20bar(%26self)%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%20implementation%20goes%20here%0A%20%20%20%20%7D%0A%0A%20%20%20%20fn%20baz(%26self)%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%20let's%20not%20worry%20about%20implementing%20baz()%20for%20now%0A%20%20%20%20%20%20%20%20unimplemented!()%3B%0A%20%20%20%20%7D%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20s%20%3D%20MyStruct%3B%0A%20%20%20%20s.bar()%3B%0A%0A%20%20%20%20%2F%2F%20we%20aren't%20even%20using%20baz()%20yet%2C%20so%20this%20is%20fine.%0A%7D%0A">Run</a></pre>
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