Re: [boost] [optional] problems with swap()

From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2008-04-11 03:38:33

Thorsten Ottosen wrote:
> Andrey Semashev skrev:
>   
>> Thorsten Ottosen wrote:
>>     
>>> Andrey Semashev skrev:
>>>       
>>>> Your approach requires the T to be default constructible which is not 
>>>> always the case. 
>>>>         
>>> Why is this better than the far more expensive copy-construction?
>>>       
>> 1. It adds a new requirement to T. 
>>     
>
> But only for swap().
>   
It's still a new requirement, which I find quite unacceptable. Suddenly 
I can't swap types without default constructors anymore?

If this variant of swap() is really more efficient, perhaps 
metaprogramming could be used to support it *if* the type has a default 
constructor. But I don't know how to detect this. TypeTraits doesn't 
contain a has_default_constructor trait. It may be that this will only 
work with 09 concepts - DefaultConstructible.

Sebastian