How to use sfinae for selecting constructors?

Question

In template meta programming, one can use SFINAE on the return type to choose a certain template member function, i.e.

template struct          


        

Answer 1

In C++11, you can use a defaulted template parameter:

template = N>::type>
explicit A(A const &);

However, if your compiler doesn't support defaulted template parameters yet, or you need multiple overloads, then you can use a defaulted function parameter like this:

template 
explicit A(A const &, typename std::enable_if= N>::type* = 0);