Reorganized docs. Minor code fix wrt opt refs

2014-06-04 18:13:06 +02:00
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+<title>Optional Reference Binding</title>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.dependencies_and_portability.optional_reference_binding"></a><a class="link" href="optional_reference_binding.html" title="Optional Reference Binding">Optional
+      Reference Binding</a>
+</h3></div></div></div>
+<p>
+        On compilers that do not conform to Standard C++ rules of reference binding,
+        operations on optional references might give adverse results: rather than
+        binding a reference to a designated object they may create an unexpected
+        temporary and bind to it. Compilers known to have these deficiencies include
+        GCC versions 4.2, 4.3, 4.4, 4.5; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0,
+        11.0, 12.0. On these compilers prefer using direct-initialization and copy
+        assignment of optional references to copy-initialization and assignment from
+        <code class="computeroutput"><span class="identifier">T</span><span class="special">&amp;</span></code>:
+      </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or2</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>  <span class="comment">// not portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>                       <span class="comment">// not portable</span>
+
+<span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;</span> <span class="identifier">or3</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>   <span class="comment">// portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;&gt;(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
+</pre>
+<p>
+        In order to check if your compiler correctly implements reference binding
+        use this test program.
+      </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cassert</span><span class="special">&gt;</span>
+
+<span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">global_i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+
+<span class="keyword">struct</span> <span class="identifier">TestingReferenceBinding</span>
+<span class="special">{</span>
+  <span class="identifier">TestingReferenceBinding</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">ii</span><span class="special">)</span>
+  <span class="special">{</span>
+    <span class="identifier">assert</span><span class="special">(&amp;</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">global_i</span><span class="special">);</span>
+  <span class="special">}</span>
+
+  <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">ii</span><span class="special">)</span>
+  <span class="special">{</span>
+    <span class="identifier">assert</span><span class="special">(&amp;</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">global_i</span><span class="special">);</span>
+  <span class="special">}</span>
+
+  <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">int</span><span class="special">&amp;&amp;)</span> <span class="comment">// remove this if your compiler doesn't have rvalue refs</span>
+  <span class="special">{</span>
+    <span class="identifier">assert</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+  <span class="special">}</span>
+<span class="special">};</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+  <span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">iref</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+  <span class="identifier">assert</span><span class="special">(&amp;</span><span class="identifier">iref</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">global_i</span><span class="special">);</span>
+
+  <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+  <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+
+  <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+  <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014 Andrzej Krzemie&#324;ski<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>
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