On Thu, Feb 04, 2016 at 01:01:10PM +0000, Jonathan Wakely wrote:
[...]
> After you mentioned this on IRC I wrote the following. I think yours
> is probably a bit simpler to read and so better, but is it worth
> taking the "unless a base class or member variable has a destructor
> that is noexcept(false)" part from mine? The noexcept on destructors
> is deduced from the destructors of bases and members, so it might be
> implicitly noexcept(true) or implicitly noexcept(false).
Ok, I didn't know that.
[...]
Thanks, I'll commit the following version.
Index: porting_to.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/porting_to.html,v
retrieving revision 1.3
diff -u -r1.3 porting_to.html
--- porting_to.html 2 Feb 2016 20:34:14 -0000 1.3
+++ porting_to.html 4 Feb 2016 13:15:15 -0000
@@ -107,6 +107,63 @@
bool valid(std::ostream& os) { return (bool)os; }
</code></pre>
+<h4>Lvalue required as left operand of assignment with complex numbers</h4>
+
+<p>
+Since C++11 (as per DR#387) the member functions <code>real()</code> and
+<code>imag()</code> of <code>std::complex</code> can no longer be used as
+lvalues, thus the following code is rejected:
+</p>
+<pre><code>
+ std::complex<double> f;
+ f.real () = val;
+</code></pre>
+
+<p>
+To assign <code>val</code> to the real component of <code>f</code>, the
+following should be used instead:
+</p>
+<pre><code>
+ std::complex<double> f;
+ f.real (val);
+</code></pre>
+
+<h4>Destructors are <code>noexcept</code> by default</h4>
+
+<p>
+As of C++11, destructors have an implicit <code>noexcept</code>
+exception-specification (unless a base class or non-static member variable has
+a destructor that is <code>noexcept(false)</code>). In practice this means
that
+the following program behaves differently in C++11 than in C++03:
+</p>
+<pre><code>
+ #include <stdexcept>
+ struct S
+ {
+ ~S() { throw std::runtime_error ("oops"); }
+ };
+ int
+ main (void)
+ {
+ try { S s; }
+ catch (...) {
+ return 42;
+ }
+ }
+</code></pre>
+
+<p>
+While in C++03 this program returns 42, in C++11 it terminates with a call to
+<code>std::terminate</code>. By default GCC will now issue a warning for
+throw-expressions in <code>noexcept</code> functions, including destructors,
+that would immediately result in a call to terminate. The new warning can be
+disabled with <tt>-Wno-terminate</tt>. It is possible to restore the old
+behavior when defining the destructor like this:
+</p>
+<pre><code>
+ ~S() noexcept(false) { throw std::runtime_error ("oops"); }
+</code></pre>
+
<h3>Header dependency changes</h3>
<p>
Marek
