id-expression: unqualified-id qualified-id
An id-expression is a restricted form of a primary-expression. [ Note: An id-expression can appear after . and -> operators. — end note ]
An id-expression that denotes a non-static data member or non-static member function of a class can only be used:
as part of a class member access in which the object expression refers to the member's class65 or a class derived from that class, or
to form a pointer to member ([expr.unary.op]), or
if that id-expression denotes a non-static data member and it appears in an unevaluated operand. [ Example:
struct S {
int m;
};
int i = sizeof(S::m); // OK
int j = sizeof(S::m + 42); // OK
— end example ]
This also applies when the object expression is an implicit (*this) ([class.mfct.non-static]).
unqualified-id: identifier operator-function-id conversion-function-id literal-operator-id ~ class-name ~ decltype-specifier template-id
An identifier is an id-expression provided it has been suitably declared (Clause [dcl.dcl]). [ Note: For operator-function-ids, see [over.oper]; for conversion-function-ids, see [class.conv.fct]; for literal-operator-ids, see [over.literal]; for template-ids, see [temp.names]. A class-name or decltype-specifier prefixed by ~ denotes a destructor; see [class.dtor]. Within the definition of a non-static member function, an identifier that names a non-static member is transformed to a class member access expression ([class.mfct.non-static]). — end note ] The type of the expression is the type of the identifier. The result is the entity denoted by the identifier. The expression is an lvalue if the entity is a function, variable, or data member and a prvalue otherwise; it is a bit-field if the identifier designates a bit-field ([dcl.struct.bind]).
qualified-id: nested-name-specifier templateopt unqualified-id
nested-name-specifier: :: type-name :: namespace-name :: decltype-specifier :: nested-name-specifier identifier :: nested-name-specifier templateopt simple-template-id ::
The type denoted by a decltype-specifier in a nested-name-specifier shall be a class or enumeration type.
A nested-name-specifier that denotes a class, optionally followed by the keyword template ([temp.names]), and then followed by the name of a member of either that class ([class.mem]) or one of its base classes, is a qualified-id; [class.qual] describes name lookup for class members that appear in qualified-ids. The result is the member. The type of the result is the type of the member. The result is an lvalue if the member is a static member function or a data member and a prvalue otherwise. [ Note: A class member can be referred to using a qualified-id at any point in its potential scope ([basic.scope.class]). — end note ] Where class-name ::~ class-name is used, the two class-names shall refer to the same class; this notation names the destructor. The form ~ decltype-specifier also denotes the destructor, but it shall not be used as the unqualified-id in a qualified-id. [ Note: A typedef-name that names a class is a class-name ([class.name]). — end note ]
The nested-name-specifier :: names the global namespace. A nested-name-specifier that names a namespace ([basic.namespace]), optionally followed by the keyword template ([temp.names]), and then followed by the name of a member of that namespace (or the name of a member of a namespace made visible by a using-directive), is a qualified-id; [namespace.qual] describes name lookup for namespace members that appear in qualified-ids. The result is the member. The type of the result is the type of the member. The result is an lvalue if the member is a function or a variable and a prvalue otherwise.
A nested-name-specifier that denotes an enumeration, followed by the name of an enumerator of that enumeration, is a qualified-id that refers to the enumerator. The result is the enumerator. The type of the result is the type of the enumeration. The result is a prvalue.
In a qualified-id, if the unqualified-id is a conversion-function-id, its conversion-type-id shall denote the same type in both the context in which the entire qualified-id occurs and in the context of the class denoted by the nested-name-specifier.