Type traits for both `type` and `const type`

Question

I'm in a need for some sort of a type trait:

template<typename T> struct foo {};
template<>
struct foo<char> { static constexpr char c = 'c' };

This works perfectly if I need a character c of the type char, but doesn't in the following case:

printf("%c", foo<const char>::c);

Is there a more elegant way to do this, rather than specify the template for both char and const char in the same way?

Answer 1

Add a partial specialization:

template <class T> struct foo<const T> : foo<T> {};