Peter Dimov wrote:
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?
(I probably snipped away too much context...) A generic function object that constructs an arbitrary type would have to know (unless having variadic templates, or being able to define operator() as a nonmember function template). This generalization would be useful to e.g. say boost::bind( constructor<T>(), 55, _2, _1) or make the implementation of the discussed Fusion utility 'construct<T>(fusion_sequence)' as simple as template<typename T, typename FusionSequence> T construct<T>(FusionSequence & seq) { return invoke_function_object( constructor<T>(), seq); } (the other stuff exists already). Regards, Tobias