Question

Possibly easy to solve, but its hard to find a solution to this:

Is it possible to (partially) specialize for a whole set of types?
In the example “Foo” should be partially specialized for (T,int) and (T,double) with only one template definition.

What I can do is define a specialisation for (T,int). See below. But, it should be for (T,int) and (T,double) with only one function definition (no code doubling).

template <typename T,typename T2>
struct Foo
{
  static inline void apply(T a, T2 b) 
  {
    cout << "we are in the generic template definition" << endl;
  }
};

// partial (T,*)
template <typename T>
struct Foo<T, int >     // here something needed like T2=(int, double)
{
  static inline void apply(T a, T2 b) 
  {
    cout << "we are in the partial specialisation for (T,int)" << endl;
  }
};

Any ideas how to partially specialize this for (T,int) and (T,double) with one template definition?

Answer 1

If I understood your question correctly, then you can write a base class template and derive from it, as illustrated below:

template <typename T, typename U>
struct Foo_Base
{
  static inline void apply(T a) 
  {
    cout << "we are in the partial specialisation Foo_Base(T)" << endl;
  }
};

template <typename T>
struct Foo<T, int> : Foo_Base<T, int> {};

template <typename T>
struct Foo<T, double> : Foo_Base<T, double> {};

Although its not one template definition (as you asked for), but you can avoid the code duplication.

Demo : http://www.ideone.com/s4anA