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| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> |
| |
| <span class="keyword">class</span> <span class="identifier">none_t</span> <span class="special">{/*</span> <span class="identifier">see</span> <span class="identifier">below</span> <span class="special">*/};</span> |
| |
| <span class="keyword">const</span> <span class="identifier">none_t</span> <span class="identifier">none</span> <span class="special">(/*</span> <span class="identifier">see</span> <span class="identifier">below</span> <span class="special">*/);</span> |
| |
| <span class="special">}</span> <span class="comment">// namespace boost</span> |
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| Class <code class="computeroutput"><span class="identifier">none_t</span></code> is meant to |
| serve as a tag for selecting appropriate overloads of from <code class="computeroutput"><span class="identifier">optional</span></code>'s interface. It is an empty, |
| trivially copyable class with disabled default constructor. |
| </p> |
| <p> |
| Constant <code class="computeroutput"><span class="identifier">none</span></code> is used to |
| indicate an optional object that does not contain a value in initialization, |
| assignment and relational operations of <code class="computeroutput"><span class="identifier">optional</span></code>. |
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