[rustc.git] / src / doc / reference / src / types / enum.md

# Enumerated types

An *enumerated type* is a nominal, heterogeneous disjoint union type, denoted
by the name of an [`enum` item]. [^enumtype]

An [`enum` item] declares both the type and a number of *variants*, each of
which is independently named and has the syntax of a struct, tuple struct or
unit-like struct.

New instances of an `enum` can be constructed with a [struct expression].

Any `enum` value consumes as much memory as the largest variant for its
corresponding `enum` type, as well as the size needed to store a discriminant.

Enum types cannot be denoted *structurally* as types, but must be denoted by
named reference to an [`enum` item].

[^enumtype]: The `enum` type is analogous to a `data` constructor declaration in
             ML, or a *pick ADT* in Limbo.

[`enum` item]: ../items/enumerations.md
[struct expression]: ../expressions/struct-expr.md
Commit	Line	Data
13cf67c4 XL	1	# Enumerated types
	2
	3	An enumerated type is a nominal, heterogeneous disjoint union type, denoted
	4	by the name of an [`enum` item]. [^enumtype]
	5
	6	An [`enum` item] declares both the type and a number of variants, each of
	7	which is independently named and has the syntax of a struct, tuple struct or
	8	unit-like struct.
	9
6a06907d	10	New instances of an `enum` can be constructed with a [struct expression].
13cf67c4 XL	11
	12	Any `enum` value consumes as much memory as the largest variant for its
	13	corresponding `enum` type, as well as the size needed to store a discriminant.
	14
	15	Enum types cannot be denoted structurally as types, but must be denoted by
	16	named reference to an [`enum` item].
	17
5869c6ff	18	[^enumtype]: The `enum` type is analogous to a `data` constructor declaration in
13cf67c4 XL	19	ML, or a pick ADT in Limbo.
13cf67c4 XL	20
416331ca	21	[`enum` item]: ../items/enumerations.md
6a06907d	22	[struct expression]: ../expressions/struct-expr.md