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<section id='main' class="content trait">
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<h1 class='fqn'><span class='in-band'>Trait <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>boxed</a>::<wbr><a class='trait' href=''>FnBox</a></span><span class='out-of-band'><span id='render-detail'>
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</span><a id='src-264' class='srclink' href='https://doc.rust-lang.org/nightly/alloc/boxed/trait.FnBox.html?gotosrc=264' title='goto source code'>[src]</a></span></h1>
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<pre class='rust trait'>pub trait FnBox<A> {
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type <a href='#associatedtype.Output' class='type'>Output</a>;
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fn <a href='#tymethod.call_box' class='fnname'>call_box</a>(self: <a class='struct' href='../../../bitflags/__core/boxed/struct.Box.html' title='bitflags::__core::boxed::Box'>Box</a><Self>, args: A) -> Self::<a class='trait' href='../../../bitflags/__core/boxed/trait.FnBox.html' title='bitflags::__core::boxed::FnBox'>Output</a>;
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}</pre><div class='stability'><em class='stab unstable'>Unstable (<code>fnbox</code>)<p>: Newly introduced</p>
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</em></div><div class='docblock'><p><code>FnBox</code> is a version of the <code>FnOnce</code> intended for use with boxed
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closure objects. The idea is that where one would normally store a
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<code>Box<FnOnce()></code> in a data structure, you should use
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<code>Box<FnBox()></code>. The two traits behave essentially the same, except
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that a <code>FnBox</code> closure can only be called if it is boxed. (Note
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that <code>FnBox</code> may be deprecated in the future if <code>Box<FnOnce()></code>
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closures become directly usable.)</p>
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<h3 id='example' class='section-header'><a href='#example'>Example</a></h3>
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<p>Here is a snippet of code which creates a hashmap full of boxed
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once closures and then removes them one by one, calling each
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closure as it is removed. Note that the type of the closures
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stored in the map is <code>Box<FnBox() -> i32></code> and not <code>Box<FnOnce() -> i32></code>.</p>
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<pre class='rust rust-example-rendered'>
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<span class='attribute'>#<span class='op'>!</span>[<span class='ident'>feature</span>(<span class='ident'>fnbox</span>)]</span>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>boxed</span>::<span class='ident'>FnBox</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>collections</span>::<span class='ident'>HashMap</span>;
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<span class='kw'>fn</span> <span class='ident'>make_map</span>() <span class='op'>-></span> <span class='ident'>HashMap</span><span class='op'><</span><span class='ident'>i32</span>, <span class='ident'>Box</span><span class='op'><</span><span class='ident'>FnBox</span>() <span class='op'>-></span> <span class='ident'>i32</span><span class='op'>>></span> {
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>map</span>: <span class='ident'>HashMap</span><span class='op'><</span><span class='ident'>i32</span>, <span class='ident'>Box</span><span class='op'><</span><span class='ident'>FnBox</span>() <span class='op'>-></span> <span class='ident'>i32</span><span class='op'>>></span> <span class='op'>=</span> <span class='ident'>HashMap</span>::<span class='ident'>new</span>();
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<span class='ident'>map</span>.<span class='ident'>insert</span>(<span class='number'>1</span>, <span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='op'>||</span> <span class='number'>22</span>));
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<span class='ident'>map</span>.<span class='ident'>insert</span>(<span class='number'>2</span>, <span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='op'>||</span> <span class='number'>44</span>));
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<span class='ident'>map</span>
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}
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<span class='kw'>fn</span> <span class='ident'>main</span>() {
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>map</span> <span class='op'>=</span> <span class='ident'>make_map</span>();
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<span class='kw'>for</span> <span class='ident'>i</span> <span class='kw'>in</span> <span class='kw-2'>&</span>[<span class='number'>1</span>, <span class='number'>2</span>] {
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<span class='kw'>let</span> <span class='ident'>f</span> <span class='op'>=</span> <span class='ident'>map</span>.<span class='ident'>remove</span>(<span class='kw-2'>&</span><span class='ident'>i</span>).<span class='ident'>unwrap</span>();
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>f</span>(), <span class='ident'>i</span> <span class='op'>*</span> <span class='number'>22</span>);
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}
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}</pre>
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</div>
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<h2 id='associated-types'>Associated Types</h2>
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<div class='methods'>
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<h3 id='associatedtype.Output' class='method stab unstable'><code>type <a href='#associatedtype.Output' class='type'>Output</a></code></h3><div class='stability'><em class='stab unstable'>Unstable (<code>fnbox</code>)<p>: Newly introduced</p>
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</em></div></div>
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<h2 id='required-methods'>Required Methods</h2>
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<div class='methods'>
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<h3 id='tymethod.call_box' class='method stab unstable'><code>fn <a href='#tymethod.call_box' class='fnname'>call_box</a>(self: <a class='struct' href='../../../bitflags/__core/boxed/struct.Box.html' title='bitflags::__core::boxed::Box'>Box</a><Self>, args: A) -> Self::<a class='trait' href='../../../bitflags/__core/boxed/trait.FnBox.html' title='bitflags::__core::boxed::FnBox'>Output</a></code></h3><div class='stability'><em class='stab unstable'>Unstable (<code>fnbox</code>)<p>: Newly introduced</p>
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