Re: [boost] Re: shifted_ptr review

From: Gregory Colvin (gregory.colvin_at_[hidden])
Date: 2003-10-01 11:38:41

On Wednesday, Oct 1, 2003, at 09:52 America/Denver, David Abrahams 
wrote:

> Gregory Colvin <gregory.colvin_at_[hidden]> writes:
>
>> Still wondering.
>>
>> On Tuesday, Sep 30, 2003, at 11:09 America/Denver, Gregory Colvin 
>> wrote:
>>> Given
>>>
>>>   template<typename T> shifted_ptr<T> make_shifted_ptr(cont T& t) {
>>>       return shifted_ptr(new(so) T(t));
>>>   }
>>>
>>>   ... make_shifted_ptr(Stuff()) ...
>>>
>>> are compilers allowed to optimize away the copy and construct the
>>> Stuff in place?
>
> The copy of the shifted_ptr?  Yes, of course.  That's the RVO.
>
>>> If so, do they?
>
> Some do; some don't.
>
> Oh, wait.  You meant the copy of Stuff()?

Yes.

>   It's not meant to be a T
> neccessarily.  It's just any old argument to T's constructor.  You
> need a bunch of overloads for make_shifted_ptr to make the example
> complete.

I was wondering if the infinite series of overloads can be dispensed 
with
in favor of requiring that T have an accessible copy constructor.  Peter
says that his compilers fail to optimize away the extra copy of T, but I
don't whether the standard allows the optimization.