6 Basic concepts [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.
If the identifier is not found, it is then looked up in the context of the entire postfix-expression and shall name a class template.
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.
For a pseudo-destructor call, the unqualified-id is looked up in the context of the complete postfix-expression.
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 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 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
]