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<section id='main' class="content struct">
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<h1 class='fqn'><span class='in-band'>Struct <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>raw</a>::<wbr><a class='struct' href=''>TraitObject</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-30565' class='srclink' href='https://doc.rust-lang.org/nightly/core/raw/struct.TraitObject.html?gotosrc=30565' title='goto source code'>[src]</a></span></h1>
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<pre class='rust struct'>pub struct TraitObject {
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pub data: <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.pointer.html'>*mut </a><a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a>,
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pub vtable: <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.pointer.html'>*mut </a><a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a>,
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}</pre><div class='stability'><em class='stab unstable'>Unstable (<code>raw</code>)</em></div><div class='docblock'><p>The representation of a trait object like <code>&SomeTrait</code>.</p>
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<p>This struct has the same layout as types like <code>&SomeTrait</code> and
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<code>Box<AnotherTrait></code>. The <a href="../../book/trait-objects.html#representation">Trait Objects chapter of the
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Book</a> contains more details about the precise nature of
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these internals.</p>
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<p><code>TraitObject</code> is guaranteed to match layouts, but it is not the
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type of trait objects (e.g. the fields are not directly accessible
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on a <code>&SomeTrait</code>) nor does it control that layout (changing the
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definition will not change the layout of a <code>&SomeTrait</code>). It is
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only designed to be used by unsafe code that needs to manipulate
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the low-level details.</p>
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<p>There is no <code>Repr</code> implementation for <code>TraitObject</code> because there
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is no way to refer to all trait objects generically, so the only
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way to create values of this type is with functions like
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<code>std::mem::transmute</code>. Similarly, the only way to create a true
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trait object from a <code>TraitObject</code> value is with <code>transmute</code>.</p>
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<p>Synthesizing a trait object with mismatched types—one where the
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vtable does not correspond to the type of the value to which the
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data pointer points—is highly likely to lead to undefined
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behavior.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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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'>raw</span>)]</span>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>mem</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>raw</span>;
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<span class='comment'>// an example trait</span>
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<span class='kw'>trait</span> <span class='ident'>Foo</span> {
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<span class='kw'>fn</span> <span class='ident'>bar</span>(<span class='kw-2'>&</span><span class='self'>self</span>) <span class='op'>-></span> <span class='ident'>i32</span>;
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}
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<span class='kw'>impl</span> <span class='ident'>Foo</span> <span class='kw'>for</span> <span class='ident'>i32</span> {
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<span class='kw'>fn</span> <span class='ident'>bar</span>(<span class='kw-2'>&</span><span class='self'>self</span>) <span class='op'>-></span> <span class='ident'>i32</span> {
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<span class='op'>*</span><span class='self'>self</span> <span class='op'>+</span> <span class='number'>1</span>
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}
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}
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<span class='kw'>let</span> <span class='ident'>value</span>: <span class='ident'>i32</span> <span class='op'>=</span> <span class='number'>123</span>;
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<span class='comment'>// let the compiler make a trait object</span>
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<span class='kw'>let</span> <span class='ident'>object</span>: <span class='kw-2'>&</span><span class='ident'>Foo</span> <span class='op'>=</span> <span class='kw-2'>&</span><span class='ident'>value</span>;
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<span class='comment'>// look at the raw representation</span>
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<span class='kw'>let</span> <span class='ident'>raw_object</span>: <span class='ident'>raw</span>::<span class='ident'>TraitObject</span> <span class='op'>=</span> <span class='kw'>unsafe</span> { <span class='ident'>mem</span>::<span class='ident'>transmute</span>(<span class='ident'>object</span>) };
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<span class='comment'>// the data pointer is the address of `value`</span>
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>raw_object</span>.<span class='ident'>data</span> <span class='kw'>as</span> <span class='op'>*</span><span class='kw'>const</span> <span class='ident'>i32</span>, <span class='kw-2'>&</span><span class='ident'>value</span> <span class='kw'>as</span> <span class='op'>*</span><span class='kw'>const</span> _);
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<span class='kw'>let</span> <span class='ident'>other_value</span>: <span class='ident'>i32</span> <span class='op'>=</span> <span class='number'>456</span>;
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<span class='comment'>// construct a new object, pointing to a different `i32`, being</span>
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<span class='comment'>// careful to use the `i32` vtable from `object`</span>
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<span class='kw'>let</span> <span class='ident'>synthesized</span>: <span class='kw-2'>&</span><span class='ident'>Foo</span> <span class='op'>=</span> <span class='kw'>unsafe</span> {
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<span class='ident'>mem</span>::<span class='ident'>transmute</span>(<span class='ident'>raw</span>::<span class='ident'>TraitObject</span> {
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<span class='ident'>data</span>: <span class='kw-2'>&</span><span class='ident'>other_value</span> <span class='kw'>as</span> <span class='op'>*</span><span class='kw'>const</span> _ <span class='kw'>as</span> <span class='op'>*</span><span class='kw-2'>mut</span> (),
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<span class='ident'>vtable</span>: <span class='ident'>raw_object</span>.<span class='ident'>vtable</span>
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})
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};
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<span class='comment'>// it should work just like we constructed a trait object out of</span>
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<span class='comment'>// `other_value` directly</span>
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>synthesized</span>.<span class='ident'>bar</span>(), <span class='number'>457</span>);</pre>
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</div><h2 class='fields'>Fields</h2>
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<table><tr class='stab unstable'>
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<td id='structfield.data'><code>data</code></td><td><div class='stability'><em class='stab unstable'>Unstable (<code>raw</code>)</em></div></td></tr><tr class='stab unstable'>
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<td id='structfield.vtable'><code>vtable</code></td><td><div class='stability'><em class='stab unstable'>Unstable (<code>raw</code>)</em></div></td></tr></table><h2 id='implementations'>Trait Implementations</h2><h3 id='derived_implementations'>Derived Implementations </h3><h3 class='impl'><code>impl <a class='trait' href='../../../bitflags/__core/marker/trait.Copy.html' title='bitflags::__core::marker::Copy'>Copy</a> for <a class='struct' href='../../../bitflags/__core/raw/struct.TraitObject.html' title='bitflags::__core::raw::TraitObject'>TraitObject</a></code></h3><div class='impl-items'></div><h3 class='impl'><code>impl <a class='trait' href='../../../bitflags/__core/clone/trait.Clone.html' title='bitflags::__core::clone::Clone'>Clone</a> for <a class='struct' href='../../../bitflags/__core/raw/struct.TraitObject.html' title='bitflags::__core::raw::TraitObject'>TraitObject</a></code></h3><div class='impl-items'><h4 id='method.clone' class='method'><code>fn <a href='../../../bitflags/__core/clone/trait.Clone.html#tymethod.clone' class='fnname'>clone</a>(&self) -> <a class='struct' href='../../../bitflags/__core/raw/struct.TraitObject.html' title='bitflags::__core::raw::TraitObject'>TraitObject</a></code></h4>
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<div class='stability'><em class='stab unstable'>Unstable (<code>raw</code>)</em></div><h4 id='method.clone_from' class='method'><span class="since">1.0.0</span><code>fn <a href='../../../bitflags/__core/clone/trait.Clone.html#method.clone_from' class='fnname'>clone_from</a>(&mut self, source: &Self)</code></h4>
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