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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="beast.ref.boost__beast__has_get_executor"></a><a class="link" href="boost__beast__has_get_executor.html" title="has_get_executor">has_get_executor</a>
  28 </h4></div></div></div>
  29 <p>
  30         <a class="indexterm" name="idm45873507331568"></a>
  31 Determine if <code class="computeroutput"><span class="identifier">T</span></code>
  32         has the <code class="computeroutput"><span class="identifier">get_executor</span></code> member
  33         function.
  34       </p>
  35 <h5>
  36 <a name="beast.ref.boost__beast__has_get_executor.h0"></a>
  37         <span class="phrase"><a name="beast.ref.boost__beast__has_get_executor.synopsis"></a></span><a class="link" href="boost__beast__has_get_executor.html#beast.ref.boost__beast__has_get_executor.synopsis">Synopsis</a>
  38       </h5>
  39 <p>
  40         Defined in header <code class="literal">&lt;<a href="../../../../../../boost/beast/core/stream_traits.hpp" target="_top">boost/beast/core/stream_traits.hpp</a>&gt;</code>
  41       </p>
  42 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  43     <span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  44 <span class="keyword">using</span> <span class="identifier">has_get_executor</span> <span class="special">=</span> <span class="emphasis"><em>see-below</em></span><span class="special">;</span>
  45 </pre>
  46 <h5>
  47 <a name="beast.ref.boost__beast__has_get_executor.h1"></a>
  48         <span class="phrase"><a name="beast.ref.boost__beast__has_get_executor.description"></a></span><a class="link" href="boost__beast__has_get_executor.html#beast.ref.boost__beast__has_get_executor.description">Description</a>
  49       </h5>
  50 <p>
  51         Metafunctions are used to perform compile time checking of template types.
  52         This type will be <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">true_type</span></code> if <code class="computeroutput"><span class="identifier">T</span></code>
  53         has the member function with the correct signature, else type will be <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">false_type</span></code>.
  54       </p>
  55 <h5>
  56 <a name="beast.ref.boost__beast__has_get_executor.h2"></a>
  57         <span class="phrase"><a name="beast.ref.boost__beast__has_get_executor.example"></a></span><a class="link" href="boost__beast__has_get_executor.html#beast.ref.boost__beast__has_get_executor.example">Example</a>
  58       </h5>
  59 <p>
  60         Use with tag dispatching:
  61       </p>
  62 <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>
  63 <span class="keyword">void</span> <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">true_type</span><span class="special">)</span>
  64 <span class="special">{</span>
  65     <span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span><span class="special">(</span>
  66         <span class="identifier">t</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">(),</span>
  67         <span class="special">[]</span>
  68         <span class="special">{</span>
  69             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Hello, world!"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
  70         <span class="special">});</span>
  71 <span class="special">}</span>
  72
  73 <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>
  74 <span class="keyword">void</span> <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">false_type</span><span class="special">)</span>
  75 <span class="special">{</span>
  76     <span class="comment">// T does not have get_executor</span>
  77 <span class="special">}</span>
  78
  79 <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>
  80 <span class="keyword">void</span> <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">t</span><span class="special">)</span>
  81 <span class="special">{</span>
  82     <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">t</span><span class="special">,</span> <span class="identifier">has_get_executor</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;{});</span>
  83 <span class="special">}</span>
  84 </pre>
  85 <p>
  86         Use with <code class="computeroutput"><span class="keyword">static_assert</span></code>:
  87       </p>
  88 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">stream</span>
  89 <span class="special">{</span>
  90     <span class="keyword">using</span> <span class="identifier">executor_type</span> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">executor_type</span><span class="special">;</span>
  91     <span class="identifier">executor_type</span> <span class="identifier">get_executor</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span>
  92 <span class="special">};</span>
  93
  94 <span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">has_get_executor</span><span class="special">&lt;</span><span class="identifier">stream</span><span class="special">&gt;::</span><span class="identifier">value</span><span class="special">,</span> <span class="string">"Missing get_executor member"</span><span class="special">);</span>
  95 </pre>
  96 <p>
  97         Convenience header <code class="literal">&lt;<a href="../../../../../../boost/beast/core.hpp" target="_top">boost/beast/core.hpp</a>&gt;</code>
  98       </p>
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