Answer by HolyBlackCat for How to create type T and value of type T template with default type T?

It's impossible to support this exact syntax (all 4 forms at the same time).

The closest thing I can think of is:

template <auto V = 0>struct Example {};

Example<int(1)> a; // Type and value.Example<int{}> a;  // Type only.Example a;         // Neither.Example<1> a;      // Value only.