[Boost-users] Determine at compile time whether type has subtraction semantics?

Subject: [Boost-users] Determine at compile time whether type has subtraction semantics?
From: John Reid (j.reid_at_[hidden])
Date: 2011-02-18 12:50:11

Is it possible to determine at compile-time if a type has subtraction 
semantics? E.g. in struct A<T> I would like to decide at compile-time 
not to execute &A::subtract in the register_fns method. Then the 
subtract method is not instantiated and there is no error.

template< typename T >
struct A {
     void register_fns() {
             &A::subtract;
     }

     T subtract( T x, T y ) {
         return x - y;
     }
};

void test() {
        A< int >().register_fns(); // int: Fine
        A< std::string >().register_fns(); // string: Compile error
}

I didn't see anything in Boost.TypeTraits

Thanks,
John.