[enum.udecl]

A using-enum-declarator of the form splice-type-specifier designates the same type designated by the splice-type-specifier.

Any other using-enum-declarator names the set of declarations found by type-only lookup ([basic.lookup.general]) for the using-enum-declarator ([basic.lookup.unqual], [basic.lookup.qual]).

The using-enum-declarator shall designate a non-dependent type with a reachable enum-specifier.

[Example 1: enum E { x }; void f() { int E; using enum E; / OK } using F = E; using enum F; / OK template<class T> using EE = T; void g() { using enum EE<E>; / OK } — end example]

A using-enum-declaration is equivalent to a using-declaration for each enumerator.

[Note 1:

A using-enum-declaration in class scope makes the enumerators of the named enumeration available via member lookup.

[Example 2: enum class fruit { orange, apple }; struct S { using enum fruit; / OK, introduces orange and apple into S }; void f() { S s; s.orange; / OK, names fruit::orange S::orange; / OK, names fruit::orange } — end example]

— end note]

[Note 2:

Two using-enum-declarations that introduce two enumerators of the same name conflict.

[Example 3: enum class fruit { orange, apple }; enum class color { red, orange }; void f() { using enum fruit; / OK using enum color; / error: color::orange and fruit::orange conflict } — end example]

— end note]

9 Declarations [dcl]

9.8 Enumerations [enum]

9.8.2 The using enum declaration [enum.udecl]