Dependent Bases and the Current Instantiation: Wording for Core Issue 1043

Proposed resolution:

Modify 14.2 [temp.names] paragraph 4 as follows:

4. When the name of a member template specialization appears after . or -> in a postfix-expression or after a nested-name-specifier in a qualified-id, and the object expression of the postfix-expression is type-dependent or the nested-name-specifier in the qualified-id depends on a template parameter (14.6.2 [temp.dep])refers to a dependent type, but the name is not does not refer to a member of the current instantiation (14.6.2.1 [temp.dep.type]), the member template name must be prefixed by the keyword template. Otherwise the name is assumed to name a non-template.

Modify 14.6 [temp.res] paragraph 3 as follows:

3. When a qualified-id is intended to refer to a type that is not a member of the current instantiation (14.6.2.1 [temp.dep.type]) and its nested-name-specifier depends on a template-parameter (14.6.2 [temp.dep])refers to a dependent type, it shall be prefixed by the keyword typename, forming a typename-specifier. If the qualified-id in a typename-specifier does not denote a type, the program is ill-formed.

Modify 14.6 [temp.res] paragraphs 6 and 7 as follows:

6. If, for a given set of template arguments, a specialization of a template is instantiated that refers to a qualified-id that denotes a type, and the nested-name-specifier of the qualified-id depends on a template parameterqualified-id refers to a member of an unknown specialization, the qualified-id shall either be prefixed by typename or shall be used in a context in which it implicitly names a type as described above.
7. Within the definition of a class template or within the definition of a member of a class template following the declarator-id, the keyword typename is not required when referring to the unqualified name of a previously declared member of the class template that declares a type. [Note: such names can be found using unqualified name lookup (3.4.1 [basic.lookup.unqual]), class member lookup (3.4.3.1 [class.qual]) into the current instantiation (14.6.2.1 [temp.dep.type]), or class member access expression lookup (3.4.5 [basic.lookup.classref]) when the type of the object expression is the current instantiation (14.6.2.2 [temp.dep.expr]). - end note]

Modify 14.6.2.1 [temp.dep.type] paragraphs 4 and 5 as follows:

4. A name is a member of the current instantiation if it is
   • An unqualified name that, when looked up, refers to at least one member of a class template the current instantiation or a non-dependent base class thereof. [Note: this can only occur when looking up a name in a scope enclosed by the definition of a class template. - end note ]
   • A qualified-id in which the nested-name-specifier refers to the current instantiation and that, when looked up, refers to at least one member of the current instantiation or a non-dependent base class thereof. [Note: if no such member is found, and the current instantiation has any dependent base classes, then the qualified-id is a member of an unknown specialization; see below. - end note]
   • An id-expression denoting the member in a class member access expression (5.2.5 [expr.ref]) for which the type of the object expression is the current instantiation, and the id-expression, when looked up (3.4.5 [basic.lookup.classref]), refers to at least one member of the current instantiation or a non-dependent base class thereof. [Note: if no such member is found, and the current instantiation has any dependent base classes, then the id-expression is a member of an unknown specialization; see below. - end note]
5. A name is a member of an unknown specialization if it is
   • the name is aA qualified-id in which the nested-name-specifier names a dependent type that is not the current instantiation.
   • A qualified-id in which the nested-name-specifier refers to the current instantiation, the current instantiation has at least one dependent base class, and name lookup of the qualified-id does not find any member of the current instantiation or a non-dependent base class thereof.
   • An id-expression denoting the member in a class member access expression (5.2.5 [expr.ref]) in which either
     • the type of the object expression is the current instantiation, the current instantiation has at least one dependent base class, and name lookup of the id-expression does not find a member of the current instantiation or a non-dependent base class thereof; or
     • the type of the object expression is dependent and is not the current instantiation.

Add the following new paragraphs after 14.6.2.1 [temp.dep.type] paragraph 5:

• If a qualified-id in which the nested-name-specifier refers to the current instantiation is not a member of the current instantiation or a member of an unknown specialization, the program is ill-formed even if the template containing the qualified-id is not instantiated; no diagnostic required. Similarly, if the id-expression in a class member access expression for which the type of the object expression is the current instantiation does not refer to a member of the current instantiation or a member of an unknown specialization, the program is ill-formed even if the template containing the member access expression is not instantiated; no diagnostic required. [Example:

  template<typename T> class A {
    typedef int type;
    void f() {
      A<T>::type i; // okay: refers to a member of the current instantiation
      typename A<T>::other j; // error: neither a member of the current instantiation nor a member of an unknown specialization
    }
  };
  

  - end example]
• If, for a given set of template arguments, a specialization of a template is instantiated that refers to a member of the current instantiation with a qualified-id or class member access expression, the name in the qualified-id or class member access expression is looked up in the template instantiation context. If the result of this lookup differs from the result of name lookup in the template definition context, name lookup is ambiguous. [Note: the result of name lookup differs only when the member of the current instantiation was found in a non-dependent base class of the current instantiation, and a member with the same name is also introduced by the substitution for a dependent base class of the current instantiation. - end note]

Modify 14.6.2.2 [temp.dep.expr] paragraph 5 as follows:

5. A class member access expression (5.2.5 [expr.ref]) is type-dependent if the expression refers to a member of the current instantiation and the type of the referenced member is dependent, or the class member access expression refers to a member of an unknown specialization. [ Note: in an expression of the form x.y or xp->y the type of the expression is usually the type of the member y of the class of x (or the class pointed to by xp). However, if x or xp refers to a dependent type that is not the current instantiation, the type of y is always dependent. If x or xp refers to a non-dependent type or refers to the current instantiation, the type of y is the type of the class member access expression. - end note ]

Modify 14.6.2.4 [temp.dep.temp] paragraph 4 as follows:

4. A template template-argument is dependent if it names a template-parameter or is a qualified-id with a nested-name-specifier which contains a class-name or a decltype-specifier that denotes a dependent typethat refers to a member of an unknown specialization.