How to Explicitly Specialize a Template Function Within a Template Class in C ?

Explicit Specialization of Template Function in a Template Class

In C , explicit specialization of a template function within a template class can be a tricky syntax issue. Consider the following code snippet:

struct tag {};

template< typename T >
struct C
{   
    template< typename Tag >
    void f( T );                 // declaration only

    template<>
    inline void f< tag >( T ) {} // ERROR: explicit specialization in non-namespace scope
};

In this example, the compiler raises an error when attempting to explicitly specialize the member function f with the tag tag. To resolve this issue, it's necessary to move the explicit specialization outside the class, but the appropriate syntax is not immediately obvious.

The provided solution suggests using a helper struct with static member functions to forward calls to the specialized member function:

template<class T, class Tag>
struct helper {
    static void f(T);   
};

template<class T>
struct helper<T, tag1> {
    static void f(T) {}
};

template<class T>
struct C {
    // ...
    template<class Tag>
    void foo(T t) {
        helper<T, Tag>::f(t);
    }
};

With this approach, the explicit specialization is contained within a non-nested struct, satisfying the requirements for explicit specialization syntax.

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