Re: [boost] [fusion] unpack into constructor?

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-06-15 10:59:51

Eric Niebler wrote:
> Tobias Schwinger wrote:
>> Tobias Schwinger wrote:
>> 
>>>         // [...] tricky nullary case with default ctor detection
>>>         // omitted for simplicity
>>> 
>> 
>> Doh! It's not possible to detect default constructibility, correct?
>> 
>> 
>> So we'd have to declare it as
>> 
>>      template<typename T, typename DefaultConstructible =
>>      mpl::false_> struct constructor;
> 
> 
> No. If the interface is "construct<T>(sequence)", then you can
> dispatch on the size of the sequence. You'd only try to default
> construct when you pass an empty sequence.

Why is there a need to detect a default constructor?