8 Expressions [expr]

8.1 Primary expressions [expr.prim]

8.1.4 Names [expr.prim.id]

id-expression:
	unqualified-id
	qualified-id
1
#
An id-expression is a restricted form of a primary-expression.
[ Note
:
An id-expression can appear after . and -> operators ([expr.ref]).
— end note
 ]
2
#
An id-expression that denotes a non-static data member or non-static member function of a class can only be used:
  • (2.1)
    as part of a class member access ([expr.ref]) in which the object expression refers to the member's class65 or a class derived from that class, or
  • (2.2)
    to form a pointer to member ([expr.unary.op]), or
  • (2.3)
    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
     ]
65)
This also applies when the object expression is an implicit (*this) ([class.mfct.non-static]).

8.1.4.1 Unqualified names [expr.prim.id.unqual]

unqualified-id:
	identifier
	operator-function-id
	conversion-function-id
	literal-operator-id
	~ class-name
	~ decltype-specifier
	template-id
1
#
An identifier is an id-expression provided it has been suitably declared (Clause [dcl.dcl]).
[ Note
:
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]).

8.1.4.2 Qualified names [expr.prim.id.qual]

qualified-id:
	nested-name-specifier template unqualified-id

nested-name-specifier:
	::
	type-name ::
	namespace-name ::
	decltype-specifier ::
	nested-name-specifier identifier ::
	nested-name-specifier template simple-template-id ::
1
#
The type denoted by a decltype-specifier in a nested-name-specifier shall be a class or enumeration type.
2
#
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 (Clause [class.derived]), 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 ([class.dtor]).
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
 ]
3
#
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.
4
#
A nested-name-specifier that denotes an enumeration ([dcl.enum]), 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.
5
#
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.