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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_typetraits.reference.is_copy_assignable"></a><a class="link" href="is_copy_assignable.html" title="is_copy_assignable">is_copy_assignable</a>
</h3></div></div></div>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_copy_assignable</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span>
</pre>
<p>
        <span class="bold"><strong>Inherits:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
        is <code class="computeroutput"><span class="identifier">CopyAssignable</span></code> (i.e. has
        an accessible explicit or implicit copy assignment operator), then inherits
        from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
        otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
        Type <code class="computeroutput"><span class="identifier">T</span></code> must be a complete
        type.
      </p>
<p>
        In other words, inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>
        only if copy assignment of <code class="computeroutput"><span class="identifier">T</span></code>
        from <code class="computeroutput"><span class="keyword">const</span> <span class="identifier">T</span>
        <span class="special">&amp;</span></code> is not marked with <code class="computeroutput"><span class="special">=</span> <span class="keyword">delete</span></code>,
        <code class="computeroutput"><span class="identifier">T</span></code> does not derives from
        <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">noncopyable</span></code> and is not marked with <code class="computeroutput"><span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code>.
      </p>
<p>
        <span class="bold"><strong>Compiler Compatibility:</strong></span> Requires the C++11
        features <code class="computeroutput"><span class="keyword">decltype</span></code> and SFINAE-expressions
        for full support.
      </p>
<p>
        If your compiler does not support C++11 deleted functions (<code class="computeroutput"><span class="special">=</span> <span class="keyword">delete</span></code>)
        or does not support SFINAE for the deleted assignments, then derive your
        classes from <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">noncopyable</span></code> or mark them with <code class="computeroutput"><span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code> to show
        that class is non-assignable.
      </p>
<p>
        Trait does not care about access modifiers, so if you see errors like this:
      </p>
<pre class="programlisting"><span class="char">'T::operator=(const T&amp;)'</span> <span class="identifier">is</span> <span class="keyword">private</span>
<span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_copy_assignable</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">:</span><span class="number">68</span><span class="special">:</span><span class="number">5</span><span class="special">:</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">within</span> <span class="keyword">this</span> <span class="identifier">context</span>
</pre>
<p>
        then you are trying to call that macro for a structure with private assignment:
      </p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">T</span> <span class="special">{</span>
    <span class="comment">// ...</span>
<span class="keyword">private</span><span class="special">:</span>
    <span class="identifier">T</span> <span class="special">&amp;</span><span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&amp;);</span>
    <span class="comment">// ...</span>
<span class="special">};</span>
</pre>
<p>
        To fix that you must modify your structure, explicitly marking it as noncopyable
        (<code class="computeroutput"><span class="special">=</span> <span class="keyword">delete</span></code>,
        <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">noncopyable</span></code> or <code class="computeroutput"><span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code>)
        or explicitly <a class="link" href="../user_defined.html" title="User Defined Specializations">specializing
        the trait</a>.
      </p>
<p>
        <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
        <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_copy_assignable</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
        or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
      </p>
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