7 Expressions [expr]

7.5 Primary expressions [expr.prim]

7.5.4 Names [expr.prim.id]

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

qualified-id:
nested-name-specifier template

_{o p t}

unqualified-id

nested-name-specifier:
::
type-name ::
namespace-name ::
decltype-specifier ::
nested-name-specifier identifier ::
nested-name-specifier template

_{o p t}

simple-template-id ::

The component names of a qualified-id are those of its nested-name-specifier and unqualified-id.

The component names of a nested-name-specifier are its identifier (if any) and those of its type-name, namespace-name, simple-template-id, and/or nested-name-specifier.

A nested-name-specifier is declarative if it is part of

(2.1)
a class-head-name,
(2.2)
an enum-head-name,
(2.3)
a qualified-id that is the id-expression of a declarator-id, or
(2.4)
a declarative nested-name-specifier.

A declarative nested-name-specifier shall not have a decltype-specifier.

A declaration that uses a declarative nested-name-specifier shall be a friend declaration or inhabit a scope that contains the entity being redeclared or specialized.

The nested-name-specifier :: nominates the global namespace.

A nested-name-specifier with a decltype-specifier nominates the type denoted by the decltype-specifier, which shall be a class or enumeration type.

If a nested-name-specifier N is declarative and has a simple-template-id with a template argument list A that involves a template parameter, let T be the template nominated by N without A.

T shall be a class template.

(3.1)
If A is the template argument list ([temp.arg]) of the corresponding template-head H ([temp.mem]), N nominates the primary template of T; H shall be equivalent to the template-head of T ([temp.over.link]).
(3.2)
Otherwise, N nominates the partial specialization ([temp.spec.partial]) of T whose template argument list is equivalent to A ([temp.over.link]); the program is ill-formed if no such partial specialization exists.

Any other nested-name-specifier nominates the entity denoted by its type-name, namespace-name, identifier, or simple-template-id.

If the nested-name-specifier is not declarative, the entity shall not be a template.

A qualified-id shall not be of the form nested-name-specifier template

_{o p t}

~ decltype-specifier nor of the form decltype-specifier :: ~ type-name.

The result of a qualified-id Q is the entity it denotes ([basic.lookup.qual]).

The type of the expression is the type of the result.

The result is an lvalue if the member is

(5.1)
a function other than a non-static member function,
(5.2)
a non-static member function if Q is the operand of a unary & operator,
(5.3)
a variable,
(5.4)
a structured binding ([dcl.struct.bind]), or
(5.5)
a data member,

and a prvalue otherwise.