[cfe-commits] interesting c++ puzzle

[Reed Kotler]

Found my pdf copy of the c++ standard 14882:2003(A).

Yep, it's all there .

Thanks.

On 01/16/2013 01:21 PM, Jordan Rose wrote:
>
> On Jan 16, 2013, at 13:12 , Krzysztof Parzyszek
> <kparzysz-sgV2jX0FEOL9JmXXK+q4OQ at public.gmane.org
> <mailto:kparzysz-sgV2jX0FEOL9JmXXK+q4OQ at public.gmane.org>> wrote:
>
>> On 1/16/2013 3:04 PM, reed kotler wrote:
>>>
>>> This seems illogical to me. It does not call the copy constructor in
>>> 5.cpp but in 6.cpp it tails
>>> to compile because it can't find a valid copy constructor.
>>
>> IIRC, according to the standard, this
>>  B b = f(1);
>> is equivalent to
>>  B b(f(1));
>>
>> I suppose the compiler refuses to treat f(1) as an object of type B&,
>> since it's a temporary.  Again, if I remember things correctly...
>
> Right, the standard requires that the copy constructor /exist,/ but
> allows the copy itself to be elided. In C++11, a move constructor would
> work here as well.
>
> C++11 [class.temporary]p1: Temporaries of class type are created in
> various contexts: ...returning a prvalue (6.6.3)…
>
> C++11 [class.copy]p31: When certain criteria are met, an implementation
> is allowed to omit the copy/move construction of a class object...in
> a return statement in a function with a class return type, when the
> expression is the name of a non-volatile automatic object (other than a
> function or catch-clause parameter) with the same cv- unqualified type
> as the function return type, the copy/move operation can be omitted by
> constructing the automatic object directly into the function’s return
> value, [and] when a temporary class object that has not been bound to a
> reference (12.2) would be copied/moved to a class object with the same
> cv-unqualified type, the copy/move operation can be omitted
> by constructing the temporary object directly into the target of the
> omitted copy/move
>
> Jordan
>
>
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