This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2023-01-15


68. Grammar does not allow "friend class A<int>;"

Section: 9.2.9.4  [dcl.type.elab]     Status: TC1     Submitter: Mike Ball     Date: 17 Oct 1998

I can't find the answer to the following in the standard. Does anybody have a reference?

The syntax for elaborated type specifier is

Which does not allow the production

    class foo<int> // foo is a template
On the other hand, a friend declaration seems to require this production,
An elaborated-type-specifier shall be used in a friend declaration for a class.*

[Footnote: The class-key of the elaborated-type-specifier is required. —end footnote]

And in 13.7.5 [temp.friend] we find the example
[Example:
    template<class T> class task;
    template<class T> task<T>* preempt(task<T>*);

    template<class T> class task {
        // ...
        friend void next_time();
        friend void process(task<T>*);
        friend task<T>* preempt<T>(task<T>*);
        template<class C> friend int func(C);

        friend class task<int>;
        template<class P> friend class frd;
        // ...
    };
Is there some special dispensation somewhere to allow the syntax in this context? Is there something I've missed about elaborated-type-specifier? Is it just another bug in the standard?

An additional problem was reported via comp.std.c++: the grammar does not allow the following example:

    namespace A{
      class B{};
    };

    namespace B{
      class A{};
      class C{
	friend class ::A::B;
      };
    };

Proposed resolution (10/00):

Change the grammar in 9.2.9.4 [dcl.type.elab] to read

and change the forms allowed in paragraph 1 to