How to Correctly Explicitly Specialize a Template Function within a C Template Class?

Explicit Specialization of Template Function in Template Class in C

In C , when working with template classes and functions, it may be necessary to explicitly specialize a template function within a template class. However, finding the correct syntax for this can be challenging.

Consider the following code:

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
};

This code, which compiles successfully in Visual C 2008 but fails in GCC 4.2, attempts to explicitly specialize the f function for the tag type within the C template class. The compiler error indicates that explicit specialization is not allowed in a non-namespace scope within the template class.

The correct way to explicitly specialize a template function within a template class is to forward calls to a member function of a partially specialized type. This can be done using a helper class:

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);
    }
};

In this code, helper is a template class with two template parameters: T (the type of the object being operated on) and Tag (the specialization tag). A partially specialized version of helper is defined for the tag1 specialization, which provides the implementation for the f function. The C template class then uses a member function foo to delegate calls to the appropriate helper::f function based on the specified tag.

The above is the detailed content of How to Correctly Explicitly Specialize a Template Function within a C Template Class?. For more information, please follow other related articles on the PHP Chinese website!