6 Basics [basic]

6.4 Name lookup [basic.lookup]

6.4.5 Class member access [basic.lookup.classref]

In a class member access expression, if the . or -> token is immediately followed by an identifier followed by a <, the identifier must be looked up to determine whether the < is the beginning of a template argument list ([temp.names]) or a less-than operator.
The identifier is first looked up in the class of the object expression ([class.member.lookup]).
If the identifier is not found, it is then looked up in the context of the entire postfix-expression and shall name a template whose specializations are types.
If the id-expression in a class member access is an unqualified-id, and the type of the object expression is of a class type C, the unqualified-id is looked up in the scope of class C ([class.member.lookup]).
If the unqualified-id is ~type-name, the type-name is looked up in the context of the entire postfix-expression.
If the type T of the object expression is of a class type C, the type-name is also looked up in the scope of class C.
At least one of the lookups shall find a name that refers to cv T.
Example
:
struct A { };

struct B {
  struct A { };
  void f(::A* a);
};

void B::f(::A* a) {
  a->~A();                      // OK: lookup in *a finds the injected-class-name
}
— end example
 ]
If the id-expression in a class member access is a qualified-id of the form
class-name-or-namespace-name::...
the class-name-or-namespace-name following the . or -> operator is first looked up in the class of the object expression ([class.member.lookup]) and the name, if found, is used.
Otherwise it is looked up in the context of the entire postfix-expression.
Note
:
See [basic.lookup.qual], which describes the lookup of a name before ​::​, which will only find a type or namespace name.
— end note
 ]
If the qualified-id has the form
::class-name-or-namespace-name::...
the class-name-or-namespace-name is looked up in global scope as a class-name or namespace-name.
If the nested-name-specifier contains a simple-template-id, the names in its template-arguments are looked up in the context in which the entire postfix-expression occurs.
If the id-expression is a conversion-function-id, its conversion-type-id is first looked up in the class of the object expression ([class.member.lookup]) and the name, if found, is used.
Otherwise it is looked up in the context of the entire postfix-expression.
In each of these lookups, only names that denote types or templates whose specializations are types are considered.
Example
:
struct A { };
namespace N {
  struct A {
    void g() { }
    template <class T> operator T();
  };
}

int main() {
  N::A a;
  a.operator A();               // calls N​::​A​::​operator N​::​A
}
— end example
 ]