How to partially specialize a class template for all derived types?

Question

I want to partially specialize an existing template that I cannot change (std::tr1::hash) for a base class and all derived classes. The reason is that I\'m usin

Answer 1

There are two variants in the following code. You could choose more appropriated for you.

template 
struct CRTPBase
{
    size_t hash() const {return 0; }
};

// First case 
//
// Help classes
struct DummyF1 {};
struct DummyF2 {};
struct DummyF3 {};
template struct X; 

// Main classes
template<> struct X : CRTPBase< X > {
    int a1;
};

template<> struct X : CRTPBase< X > {
    int b1;
};

// typedefs
typedef X F1;
typedef X F2;
typedef DummyF3    F3; // Does not work

namespace std { namespace tr1 {
    template
    struct hash< X > {
        size_t operator()(const CRTPBase< X > & base) const     
        {         
            return base.hash();     
        }
    };
}} // namespace tr1 // namespace std 

//

// Second case
struct DummyS1 : CRTPBase  {
    int m1;
};
//
template 
struct Y : T {};
//
typedef Y S1;


namespace std { namespace tr1 {
    template
    struct hash< Y > {
        size_t operator()(const CRTPBase & base) const     
        {         
            return base.hash();     
        }
    };
}} // namespace tr1 // namespace std 

void main1()
{
    using std::tr1::hash;
    F1 f1;
    F2 f2;
    F3 f3;
    hash hf1; size_t v1 = hf1(f1); // custom hash functor
    hash hf2; size_t v2 = hf2(f2); // custom hash functor
    hash hf3; size_t v3 = hf3(f3); // error: standard hash functor

    S1 s1;
    hash hs1; size_t w1 = hs1(s1); // custom hash functor

}