On Monday, 4 November 2013 at 11:41:04 UTC, Lars T. Kyllingstad
wrote:
On Monday, 4 November 2013 at 07:17:12 UTC, monarch_dodra wrote:
http://d.puremagic.com/issues/show_bug.cgi?id=11287
According to the conversation, NRVO is supposed to be part of
the spec, and you should expect it to work.
I'm not an expert, but aren't there cases where NRVO can't be
applied? For example:
S foo()
{
S s1;
// Initialize s1
S s2;
// Initialize s2
if (someCondition) return s1;
else return s2;
}
However, the return value can always be *moved*.
According to Andrei
(http://video.ch9.ms/sessions/gonat/2013/AndreiQuickCodeGn13.zip
slide 37), NRVO requires "All paths return same local". If not,
"assume an extra copy".
IMO "assume" means that the compiler *may* elide the copy, but
*that* would be an optimization. If all your paths return the
same named local, then NRVO should be guaranteed.
But I think the spec should formalize the behavior.
