ceph/src/boost/libs/optional/doc/html/boost_optional/examples.html

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  27 <a name="boost_optional.examples"></a><a class="link" href="examples.html" title="Examples">Examples</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="examples.html#boost_optional.examples.optional_return_values">Optional
  31       return values</a></span></dt>
  32 <dt><span class="section"><a href="examples.html#boost_optional.examples.optional_local_variables">Optional
  33       local variables</a></span></dt>
  34 <dt><span class="section"><a href="examples.html#boost_optional.examples.optional_data_members">Optional
  35       data members</a></span></dt>
  36 <dt><span class="section"><a href="examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction">Bypassing
  37       expensive unnecessary default construction</a></span></dt>
  38 </dl></div>
  39 <div class="section">
  40 <div class="titlepage"><div><div><h3 class="title">
  41 <a name="boost_optional.examples.optional_return_values"></a><a class="link" href="examples.html#boost_optional.examples.optional_return_values" title="Optional return values">Optional
  42       return values</a>
  43 </h3></div></div></div>
  44 <pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">get_async_input</span><span class="special">()</span>
  45 <span class="special">{</span>
  46     <span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">queue</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()</span> <span class="special">)</span>
  47         <span class="keyword">return</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;(</span><span class="identifier">queue</span><span class="special">.</span><span class="identifier">top</span><span class="special">());</span>
  48     <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;();</span> <span class="comment">// uninitialized</span>
  49 <span class="special">}</span>
  50
  51 <span class="keyword">void</span> <span class="identifier">receive_async_message</span><span class="special">()</span>
  52 <span class="special">{</span>
  53     <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">rcv</span> <span class="special">;</span>
  54     <span class="comment">// The safe boolean conversion from 'rcv' is used here.</span>
  55     <span class="keyword">while</span> <span class="special">(</span> <span class="special">(</span><span class="identifier">rcv</span> <span class="special">=</span> <span class="identifier">get_async_input</span><span class="special">())</span> <span class="special">&amp;&amp;</span> <span class="special">!</span><span class="identifier">timeout</span><span class="special">()</span> <span class="special">)</span>
  56         <span class="identifier">output</span><span class="special">(*</span><span class="identifier">rcv</span><span class="special">);</span>
  57 <span class="special">}</span>
  58 </pre>
  59 </div>
  60 <div class="section">
  61 <div class="titlepage"><div><div><h3 class="title">
  62 <a name="boost_optional.examples.optional_local_variables"></a><a class="link" href="examples.html#boost_optional.examples.optional_local_variables" title="Optional local variables">Optional
  63       local variables</a>
  64 </h3></div></div></div>
  65 <pre class="programlisting"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">name</span> <span class="special">;</span>
  66 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">database</span><span class="special">.</span><span class="identifier">open</span><span class="special">()</span> <span class="special">)</span>
  67 <span class="special">{</span>
  68     <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">database</span><span class="special">.</span><span class="identifier">lookup</span><span class="special">(</span><span class="identifier">employer_name</span><span class="special">)</span> <span class="special">;</span>
  69 <span class="special">}</span>
  70 <span class="keyword">else</span>
  71 <span class="special">{</span>
  72     <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">can_ask_user</span> <span class="special">)</span>
  73         <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">user</span><span class="special">.</span><span class="identifier">ask</span><span class="special">(</span><span class="identifier">employer_name</span><span class="special">)</span> <span class="special">;</span>
  74 <span class="special">}</span>
  75
  76 <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">name</span> <span class="special">)</span>
  77     <span class="identifier">print</span><span class="special">(*</span><span class="identifier">name</span><span class="special">);</span>
  78 <span class="keyword">else</span> <span class="identifier">print</span><span class="special">(</span><span class="string">"employer's name not found!"</span><span class="special">);</span>
  79 </pre>
  80 </div>
  81 <div class="section">
  82 <div class="titlepage"><div><div><h3 class="title">
  83 <a name="boost_optional.examples.optional_data_members"></a><a class="link" href="examples.html#boost_optional.examples.optional_data_members" title="Optional data members">Optional
  84       data members</a>
  85 </h3></div></div></div>
  86 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">figure</span>
  87 <span class="special">{</span>
  88     <span class="keyword">public</span><span class="special">:</span>
  89
  90     <span class="identifier">figure</span><span class="special">()</span>
  91     <span class="special">{</span>
  92         <span class="comment">// data member 'm_clipping_rect' is uninitialized at this point.</span>
  93     <span class="special">}</span>
  94
  95     <span class="keyword">void</span> <span class="identifier">clip_in_rect</span> <span class="special">(</span> <span class="identifier">rect</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">rect</span> <span class="special">)</span>
  96     <span class="special">{</span>
  97         <span class="special">....</span>
  98         <span class="identifier">m_clipping_rect</span> <span class="special">=</span> <span class="identifier">rect</span> <span class="special">;</span> <span class="comment">// initialized here.</span>
  99     <span class="special">}</span>
 100
 101     <span class="keyword">void</span> <span class="identifier">draw</span> <span class="special">(</span> <span class="identifier">canvas</span><span class="special">&amp;</span> <span class="identifier">cvs</span> <span class="special">)</span>
 102     <span class="special">{</span>
 103         <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">m_clipping_rect</span> <span class="special">)</span>
 104             <span class="identifier">do_clipping</span><span class="special">(*</span><span class="identifier">m_clipping_rect</span><span class="special">);</span>
 105
 106         <span class="identifier">cvs</span><span class="special">.</span><span class="identifier">drawXXX</span><span class="special">(..);</span>
 107     <span class="special">}</span>
 108
 109     <span class="comment">// this can return NULL.</span>
 110     <span class="identifier">rect</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_clipping_rect</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">m_clipping_rect</span><span class="special">);</span> <span class="special">}</span>
 111
 112     <span class="keyword">private</span> <span class="special">:</span>
 113
 114     <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">rect</span><span class="special">&gt;</span> <span class="identifier">m_clipping_rect</span> <span class="special">;</span>
 115
 116 <span class="special">};</span>
 117 </pre>
 118 </div>
 119 <div class="section">
 120 <div class="titlepage"><div><div><h3 class="title">
 121 <a name="boost_optional.examples.bypassing_expensive_unnecessary_default_construction"></a><a class="link" href="examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction" title="Bypassing expensive unnecessary default construction">Bypassing
 122       expensive unnecessary default construction</a>
 123 </h3></div></div></div>
 124 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">ExpensiveCtor</span> <span class="special">{</span> <span class="special">...</span> <span class="special">}</span> <span class="special">;</span>
 125 <span class="keyword">class</span> <span class="identifier">Fred</span>
 126 <span class="special">{</span>
 127     <span class="identifier">Fred</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">mLargeVector</span><span class="special">(</span><span class="number">10000</span><span class="special">)</span> <span class="special">{}</span>
 128
 129     <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">ExpensiveCtor</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">mLargeVector</span> <span class="special">;</span>
 130 <span class="special">}</span> <span class="special">;</span>
 131 </pre>
 132 </div>
 133 </div>
 134 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 135 <td align="left"></td>
 136 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014 Andrzej Krzemie&#324;ski<p>
 137         Distributed under the Boost Software License, Version 1.0. (See accompanying
 138         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 139       </p>
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