Re: [Boost-users] enable_if catch all?

Subject: Re: [Boost-users] enable_if catch all?
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2009-07-19 17:22:18

Zachary Turner wrote:
> Supposing I have 4 or 5 mutually exclusive overloads of a function
> using enable_if as a function parameter with a default argument, is
> there any way for me to provide an additional version of this function
> that handles every other case, without manually combining all the
> previous cases and using another enable_if?
> 
> For example:
> 
> template<class T>
> void foo(typename enable_if<condition1>::type* dummy=0) {}
> 
> template<class T>
> void foo(typename enable_if<condition2>::type* dummy=0) {}
> 
> template<class T>
> void foo(typename enable_if<condition3>::type* dummy=0) {}
> 
> template<class T>
> void foo(typename enable_if<condition4>::type* dummy=0) {}
> 
> template<class T>
> void foo()
> {
>    //default instantiation that gets invoked if and only if all of the
> other overloads fail
> }

template<class T>
void foo(...)
{
     //default instantiation that gets invoked if and only if all of the
 > other overloads fail
}

Note, however, it will only work if you call foo<T>(0) and not if you 
call foo<T>().