Re: C++0x: returning rvalue references, recycling temporaries
On 13 sep, 04:28, Howard Hinnant <howard.hinn...@gmail.com> wrote:
Consider:
string operator+(const string&, const string&);
string&& operator+(string&& x, const string& y) {x += y; return x;}
const string& d = a + b + c;
"a+b" forms a temporary string which then binds to "x" in the second op
+ overload. That temporary is appended to and then returned by rvalue
ref. d now refers to the temporary created by "a+b" and modified by
"+= c". The life time of that temporary ends at the semicolon after
"c". So d is a dangling reference.
When I read 8.5.3.5, it looks like it says that d does not refer to
the temporary created by a+b but to a newly created temporary that
gets initialized from the rvalue-ref. But if you say different, I
trust you.
Would there be any ill effect to changing the standard so that the
lifetime extension of 12.2 also applies to this case? It looks like a
fairly natural expectation.
For the cost of an extra move construction (after an append) you can
sleep better at night. :-)
Suboptimal solutions prevent me from sleeping well :-(
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