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- <a name="boost_optional.dependencies_and_portability.emplace_operations_in_older_compilers"></a><a class="link" href="emplace_operations_in_older_compilers.html" title="Emplace operations in older compilers">Emplace
- operations in older compilers</a>
- </h3></div></div></div>
- <p>
- <a name="optional_emplace_workaround"></a>Certain constructors and functions
- in the interface of <code class="computeroutput"><span class="identifier">optional</span></code>
- perform a 'perfect forwarding' of arguments:
- </p>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">);</span>
- </pre>
- <p>
- On compilers that do not support variadic templates, each of these functions
- is substituted with two overloads, one forwarding a single argument, the
- other forwarding zero arguments. This forms the following set:
- </p>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">();</span>
- </pre>
- <p>
- On compilers that do not support rvalue references, each of these functions
- is substituted with three overloadss: taking <code class="computeroutput"><span class="keyword">const</span></code>
- and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference,
- and third forwarding zero arguments. This forms the following set:
- </p>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
- <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">();</span>
- </pre>
- <p>
- This workaround addressess about 40% of all use cases. If this is insufficient,
- you need to resort to using <a class="link" href="../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
- Factories</a>.
- </p>
- </div>
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- <td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- 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>)
- </p>
- </div></td>
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