James Dennett ha scritto:
> Ondra Holub wrote:
>>
>> A fn()
>> {
>>     return A(ctor parameters);
>> }
>>
>> Is it ensured by standard, that copy constructor of A is not called or
>> is it only common optimization?
>
> It is not guaranteed, though the standard does permit an
> implementation to elide the copy in this case (and it is
> indeed a common, maybe even now universal, optimization).
>

Moreover, even in the case the copy is elided, the copy constructor
must be accessible. The copy still occurs semantically although the copy
constructor may not be actually called.

Ganesh

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James Dennett wrote:

>> Is it ensured by standard, that copy constructor of A is not called or
>> is it only common optimization?
>
> It is not guaranteed, though the standard does permit an
> implementation to elide the copy in this case (and it is
> indeed a common, maybe even now universal, optimization).
>

Note that even when elided, the copy constructor must be accessible
as if it were going to be used.

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Ondra Holub wrote:
> Hello all.
>
> when I have some class
>
> class A
> {
> // Some stuff
> };
>
> And I need to return instance of this class (not reference, nor
> pointer) from some function
>
> A fn()
> {
>     return A(ctor parameters);
> }
>
> Is it ensured by standard, that copy constructor of A is not called or
> is it only common optimization?

It is not guaranteed, though the standard does permit an
implementation to elide the copy in this case (and it is
indeed a common, maybe even now universal, optimization).

-- James

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