C++ why does SFINAE fail with only a class template parameter?

Question

I\'m using SFINAE in the style of this answer in order to call a generic vector object by using an appropriate member function. For example, the following code calls o

Answer 1

In your failing example, the template parameter VectorType has already been determined by the time get is being resolved. To make SFINAE work, you need to make the template parameters you are using for SFINAE resolve at that method call. The following is a modification of your first example to work like you want to:

template struct rank : rank { static_assert(I > 0, ""); };
template<> struct rank<0> {};

template
struct VectorWrapper
{
    auto get(int i) const
    {
        return get(v, i, rank<5>());
    }

    template::value> >
    auto get(int i, rank<2>) const
    {
        return v[i];
    }

    template::value> >
    auto get(int i, rank<1>) const
    {
        return v(i);
    }

    VectorType v;
};

This way, V is resolved when get is called, and it will correctly use SFINAE.