Why Does Explicit Specialization of Template Functions Fail in Non-Namespace-Scoped Template Classes in C ?

Explicit Specialization of Template Functions in Template Classes in C

Error:

Developers attempting to explicitly specialize template functions within non-namespace-scoped template classes may encounter compilation errors in GCC. The following code exhibits such an issue:

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 'structC<T>'

Resolution:

Explicit specialization of member functions is not supported in non-namespace-scoped template classes. Instead, consider forwarding calls to a member function of a partially specialized intermediary type:

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);
    }
};

This approach leverages partial template specialization to achieve the desired behavior while adhering to the syntactic requirements of GCC.

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