This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-04-13

531. Defining members of explicit specializations

[Voted into the WP at the March, 2011 meeting as part of paper N3262.]

The Standard does not fully describe the syntax to be used when a member of an explicitly-specialized member class or member class template is defined in namespace scope. 13.9.4 [temp.expl.spec] paragraph 4 says that the “explicit specialization syntax” (presumably referring to “template<>”) is not used in defining a member of an explicit specialization when a class template is explicitly specialized as a class. However, nothing is said anywhere about how to define a member of a specialization when:

1. the entity being specialized is a class (member of a template class) rather than a class template.

2. the result of the specialization is a class template rather than a class (cf 13.9.4 [temp.expl.spec] paragraph 18, which describes this case as a “member template that... remain[s] unspecialized”).

(See paper J16/05-0148 = WG21 N1888 for further details, including a survey of existing implementation practice.)

Notes from the October, 2005 meeting:

The CWG felt that the best approach, balancing consistency with implementation issues and existing practice, would be to require that template<> be used when defining members of all explicit specializations, including those currently covered by 13.9.4 [temp.expl.spec] paragraph 4.

Proposed resolution (February, 2010) [SUPERSEDED]:

Change 13.9.4 [temp.expl.spec] paragraph 5 as follows:

...The definition of an explicitly specialized class is unrelated to the definition of a generated specialization. That is, its members need not have the same names, types, etc. as the members of a generated specialization. Definitions of members of an explicitly specialized class are defined in the same manner as members of normal classes, and not using the syntax for explicit specialization . [Example:

    template<class T> struct A {
      void f(T) { /* ... */ }

    };
    template<> struct A<int> {
      void f(int);

    };
    void h() {
      A<int> a;
      a.f(16); // A<int>::f must be defined somewhere
    }
    // explicit specialization syntax not used for a member of
    // explicitly specialized class template specialization

    void A<int>::f(int) { /* ... */ }

—end example]

Note (June, 2010):

Because the survey of implementations on which the CWG relied in reaching this resolution is quite old, a new survey of current practice is needed.