Partial custom function template with argument template

Question

I have a template function (for simplicity, let it "add")

template<typename T>
inline T add(const T a, const T b)
{
    return a+b;
}

I can specialize it for certain types, but what I would like to do is specialize in a template type.

In my case, my template type is called Vec2<T>. This is a two-dimensional trigonometric vector (both in x and y, not a C ++ vector!)

What I would like to do is specialize in my function addfor the general case Vec2<T>, and not specialize in each type with which it can be used Vec2.

The library from which it Vec2<T>comes has typedefs for V2d(double), V2f(float) and V2i(int).

I can specialize for each of them using something like:

template<>
inline V2f add<V2f>(const V2f a, const V2f b)
{
    return V2f(a.x + b.x, a.y + b.y);
}

, , , - :

template<typename S>
inline Vec2<S> add<Vec2<S> >(const Vec2<S> a, const Vec2<S> b)
{
    return Vec2<S>(a.x + b.x, a.y + b.y);
}

, , .

Answer 1

( ). :

template<typename S>
inline Vec2<S> add(const Vec2<S>& a, const Vec2<S>& b)
{
    return Vec2<S>(a.x + b.x, a.y + b.y);
}

, add Vec2 .

---

pass-by-const-reference, .

Answer 2

. , , , :

template<typename> struct add_impl;

template<typename T>
T add(const T a, const T b)
{
    return add_impl<T>::do_it(a, b);
}

template<typename T>
struct add_impl {
  static T do_it(const T a, const T b) { return a + b; }
};

template<typename S>
struct add_impl<Vec2<S> > {
  static Vec2<S> do_it(const Vec2<S> a, const Vec2<S> b) { 
    return Vec2<S>(a.x + b.x, a.y + b.y);
  }
};