Question

A class can expose types without instantiating it. For example:

class bar {
  typedef int GET_TYPE;
};

template<class T>
void foo() {
  typename T::GET_TYPE t;
  // do something with t
}

foo<bar>();

Can a integer number be exposed in a similar way? In the sense that template parameters can be either types or built-in types.

Answer 1

enum is good for that.

class bar
{
     enum { MyNumericValue = 17, };
};

This only works for integral values, but works with all versions of C++.

For non-integral values, see CatPlusPlus’s modern solution (C++11-only).