Re: [wwwdocs] Document C++ DR 1579 in /gcc-5/porting_to.html

[Sandra Loosemore]

On 03/10/2015 11:43 AM, Jonathan Wakely wrote:

+<h3>Return by converting move constructor</h3>
+
+<p>GCC 5 implements
+<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1579";>DR 
1579</a>
+which means that in a function like:</p>
+
+<pre><code>
+  X
+  foo()
+  {
+    Y y;
+    return y;
+  }
+</code></pre>
+
+<p>GCC will first attempt to construct the return value as if <code>y</code>
+were an rvalue, and if that fails then it will try again for an lvalue
+(all C++11 compilers already do this when returning a variable of the
+same type as the function returns, but now they are required to do it
+when the types are not the same).
+This will change the constructor that gets called in some cases,
+for example it might now call <code>X(Y&amp;&amp;)</code> instead of
+<code>X(const Y&amp;)</code>.
+</p>
+<p>
+In most cases the only observable difference will be code that runs faster
+(by moving instead of copying) but if it causes a problem the new behavior
+can be prevented by ensuring the compiler treats <code>y</code> as an lvalue,
+using <code>return X(y);</code> or
+<code>return static_cast&lt;Y&amp;&gt;(y);</code>.
+</p>
+

Errrmmmm.  If GCC 5 implements (present tense) this new feature, why is 
the description written mostly in the future tense?  :-(

-Sandra the grammar geek