Re: c++/8665: explicit specialization of the member class template of a class template

[reichelt at igpm dot rwth-aachen dot de]

Synopsis: explicit specialization of the member class template of a class template

State-Changed-From-To: open->closed
State-Changed-By: reichelt
State-Changed-When: Thu Nov 21 14:00:58 2002
State-Changed-Why:
    Not a bug.
    
    GCC is right: your code *is* ill-formed.
    Actually, there are two bugs in your code. The first one is, that you try
    to do the specialization inside the class (in the following example A is a
    normal class instead of a templated one as in your example):
    
    struct A
    {
        template <class X_> struct B       {};
        template <>         struct B<char> {};  // wrong
    };
    
    template <> struct A::B<char> {};           // right
    
    This is because of 14.7.3.2:
    AN EXPLICIT SPECIALIZATION SHALL BE DECLARED in the namespace of which the
    template is a member, or, for member templates, IN THE NAMESPACE OF WHICH
    THE ENCLOSING CLASS or enclosing class template IS A MEMBER.
    An explicit specialization of a member function, member class or static
    data member of a class template shall be declared in the namespace of
    which the class template is a member.
    
    Because you do the specialization in the class instead of the surrounding
    namespace (which is the global one in this case) you get the message:
    exptmpl.cpp:15: explicit specialization in non-namespace scope `struct A<T_>'
    
    
    The second bug is, that you try to explicitly specialize B without
    specializing A first - this is not allowed (see 14.7.3.18, especially
    the last two lines of the example).
    
    That's why you get the message:
    exptmpl.cpp:15: enclosing class templates are not explicitly specialized
    
    The rest of the error message is just fallout from the ill-formed
    code above.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8665