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Added limited emplace() for older compilers

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Andrzej Krzemienski
2014-06-06 23:24:43 +02:00
parent dec71d338d
commit fdc98d17ca
12 changed files with 612 additions and 29 deletions
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doc/html/boost_optional/quick_start/optional_data_members.html
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@ -53,13 +53,15 @@
<code class="computeroutput"><span class="identifier">optional</span></code>'s default constructor
creates an uninitialized optional. No call to <code class="computeroutput"><span class="identifier">Resource</span></code>'s
default constructor is attempted. <code class="computeroutput"><span class="identifier">Resource</span></code>
doesn't have to be <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top">Default
Constructible</a>. In function <code class="computeroutput"><span class="identifier">getResource</span></code>
we first check if <code class="computeroutput"><span class="identifier">resource_</span></code>
is initialized. This time we do not use the contextual conversion to <code class="computeroutput"><span class="keyword">bool</span></code>, but a comparison with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>. These two ways are equivalent. Function
<code class="computeroutput"><span class="identifier">emplace</span></code> initializes the optional
in-place by perfect-forwarding the arguments to the constructor of <code class="computeroutput"><span class="identifier">Resource</span></code>. No copy- or move-construction
is involved here. <code class="computeroutput"><span class="identifier">Resource</span></code>
doesn't have to be <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">DefaultConstructible</span></code></a>. In function
<code class="computeroutput"><span class="identifier">getResource</span></code> we first check
if <code class="computeroutput"><span class="identifier">resource_</span></code> is initialized.
This time we do not use the contextual conversion to <code class="computeroutput"><span class="keyword">bool</span></code>,
but a comparison with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>.
These two ways are equivalent. Function <code class="computeroutput"><span class="identifier">emplace</span></code>
initializes the optional in-place by perfect-forwarding the arguments to
the constructor of <code class="computeroutput"><span class="identifier">Resource</span></code>.
No copy- or move-construction is involved here. <code class="computeroutput"><span class="identifier">Resource</span></code>
doesn't even have to be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
</p>
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