Enumerated types

An enumerated type is a nominal, heterogeneous disjoint union type, denoted by the name of an enum item. 1

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.


The enum type is analogous to a data constructor declaration in ML, or a pick ADT in Limbo.