Title
Partial specialization on member function types
Status
c++11
Section
9.3.4.6 [dcl.fct]
Submitter
Peter Dimov

Created on 2005-11-04.00:00:00 last changed 96 months ago

Messages

Date: 2011-03-15.00:00:00

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

Date: 2008-06-15.00:00:00

Proposed resolution (June, 2008) [SUPERSEDED]:

Change 9.3.4.6 [dcl.fct] paragraph 7 as follows:

A cv-qualifier-seq shall only be part of the function type for a non-static member function, the function type to which a pointer to member refers, or the top-level function type of a function typedef declaration, or the top-level function type of a type-id that is a template-argument for a type template-parameter. The effect... A ref-qualifier shall only be part of the function type for a non-static member function, the function type to which a pointer to member refers, or the top-level function type of a function typedef declaration, or the top-level function type of a type-id that is a template-argument for a type template-parameter. The return type...
Date: 2006-04-15.00:00:00

Notes from the April, 2006 meeting:

During the meeting the CWG was of the opinion that the “R() const” specialization would not match the const member function even if it were allowed and so classified the issue as NAD. Questions have been raised since the meeting, however, suggesting that the template argument in the partial specialization would, in fact, match the type of a const member function (see, for example, the very similar usage via typedefs in 11.4.2 [class.mfct] paragraph 9). The issue is thus being left open for renewed discussion at the next meeting.

Date: 2005-11-04.00:00:00

The following example appears to be well-formed, with the partial specialization matching the type of Y::f(), even though it is rejected by many compilers:

    template<class T> struct X;

    template<class R> struct X< R() > {
    };

    template<class F, class T> void test(F T::* pmf) {
        X<F> x;
    }

    struct Y {
        void f() {
        }
    };

    int main() {
        test( &Y::f );
    }

However, 9.3.4.6 [dcl.fct] paragraph 4 says,

A cv-qualifier-seq shall only be part of the function type for a non-static member function, the function type to which a pointer to member refers, or the top-level function type of a function typedef declaration. The effect of a cv-qualifier-seq in a function declarator is not the same as adding cv-qualification on top of the function type. In the latter case, the cv-qualifiers are ignored.

This specification makes it impossible to write a partial specialization for a const member function:

    template<class R> struct X<R() const> {
    };

A template argument is not one of the permitted contexts for cv-qualification of a function type. This restriction should be removed.

History
Date User Action Args
2014-03-03 00:00:00adminsetstatus: fdis -> c++11
2011-04-10 00:00:00adminsetmessages: + msg3341
2011-04-10 00:00:00adminsetstatus: review -> fdis
2008-06-29 00:00:00adminsetmessages: + msg1700
2008-06-29 00:00:00adminsetstatus: drafting -> review
2006-11-05 00:00:00adminsetstatus: open -> drafting
2006-04-22 00:00:00adminsetmessages: + msg1353
2005-11-04 00:00:00admincreate