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<p class='location'><a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>mem</a></p><script>window.sidebarCurrent = {name: 'drop', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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<h1 class='fqn'><span class='in-band'>Function <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>mem</a>::<wbr><a class='fn' href=''>drop</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a id='src-5620' class='srclink' href='https://doc.rust-lang.org/nightly/core/mem/fn.drop.html?gotosrc=5620' title='goto source code'>[src]</a></span></h1>
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<pre class='rust fn'>pub fn drop<T>(_x: T)</pre><span class="since">1.0.0</span><div class='docblock'><p>Disposes of a value.</p>
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<p>While this does call the argument's implementation of <code>Drop</code>, it will not
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release any borrows, as borrows are based on lexical scope.</p>
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<p>This effectively does nothing for
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<a href="../../book/ownership.html#copy-types">types which implement <code>Copy</code></a>,
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e.g. integers. Such values are copied and <em>then</em> moved into the function,
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so the value persists after this function call.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<p>Basic usage:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>let</span> <span class='ident'>v</span> <span class='op'>=</span> <span class='macro'>vec</span><span class='macro'>!</span>[<span class='number'>1</span>, <span class='number'>2</span>, <span class='number'>3</span>];
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<span class='ident'>drop</span>(<span class='ident'>v</span>); <span class='comment'>// explicitly drop the vector</span></pre>
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<p>Borrows are based on lexical scope, so this produces an error:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>v</span> <span class='op'>=</span> <span class='macro'>vec</span><span class='macro'>!</span>[<span class='number'>1</span>, <span class='number'>2</span>, <span class='number'>3</span>];
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<span class='kw'>let</span> <span class='ident'>x</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='ident'>v</span>[<span class='number'>0</span>];
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<span class='ident'>drop</span>(<span class='ident'>x</span>); <span class='comment'>// explicitly drop the reference, but the borrow still exists</span>
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<span class='ident'>v</span>.<span class='ident'>push</span>(<span class='number'>4</span>); <span class='comment'>// error: cannot borrow `v` as mutable because it is also</span>
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<span class='comment'>// borrowed as immutable</span></pre>
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<p>An inner scope is needed to fix this:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>v</span> <span class='op'>=</span> <span class='macro'>vec</span><span class='macro'>!</span>[<span class='number'>1</span>, <span class='number'>2</span>, <span class='number'>3</span>];
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{
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<span class='kw'>let</span> <span class='ident'>x</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='ident'>v</span>[<span class='number'>0</span>];
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<span class='ident'>drop</span>(<span class='ident'>x</span>); <span class='comment'>// this is now redundant, as `x` is going out of scope anyway</span>
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}
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<span class='ident'>v</span>.<span class='ident'>push</span>(<span class='number'>4</span>); <span class='comment'>// no problems</span></pre>
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<p>Since <code>RefCell</code> enforces the borrow rules at runtime, <code>drop()</code> can
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seemingly release a borrow of one:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>cell</span>::<span class='ident'>RefCell</span>;
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<span class='kw'>let</span> <span class='ident'>x</span> <span class='op'>=</span> <span class='ident'>RefCell</span>::<span class='ident'>new</span>(<span class='number'>1</span>);
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>mutable_borrow</span> <span class='op'>=</span> <span class='ident'>x</span>.<span class='ident'>borrow_mut</span>();
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<span class='op'>*</span><span class='ident'>mutable_borrow</span> <span class='op'>=</span> <span class='number'>1</span>;
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<span class='ident'>drop</span>(<span class='ident'>mutable_borrow</span>); <span class='comment'>// relinquish the mutable borrow on this slot</span>
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<span class='kw'>let</span> <span class='ident'>borrow</span> <span class='op'>=</span> <span class='ident'>x</span>.<span class='ident'>borrow</span>();
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<span class='macro'>println</span><span class='macro'>!</span>(<span class='string'>"{}"</span>, <span class='op'>*</span><span class='ident'>borrow</span>);</pre>
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<p>Integers and other types implementing <code>Copy</code> are unaffected by <code>drop()</code></p>
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<pre class='rust rust-example-rendered'>
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<span class='attribute'>#[<span class='ident'>derive</span>(<span class='ident'>Copy</span>, <span class='ident'>Clone</span>)]</span>
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<span class='kw'>struct</span> <span class='ident'>Foo</span>(<span class='ident'>u8</span>);
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<span class='kw'>let</span> <span class='ident'>x</span> <span class='op'>=</span> <span class='number'>1</span>;
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<span class='kw'>let</span> <span class='ident'>y</span> <span class='op'>=</span> <span class='ident'>Foo</span>(<span class='number'>2</span>);
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<span class='ident'>drop</span>(<span class='ident'>x</span>); <span class='comment'>// a copy of `x` is moved and dropped</span>
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<span class='ident'>drop</span>(<span class='ident'>y</span>); <span class='comment'>// a copy of `y` is moved and dropped</span>
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<span class='macro'>println</span><span class='macro'>!</span>(<span class='string'>"x: {}, y: {}"</span>, <span class='ident'>x</span>, <span class='ident'>y</span>.<span class='number'>0</span>); <span class='comment'>// still available</span></pre>
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