r[type.enum]
r[type.enum.intro] An enumerated type is a nominal, heterogeneous disjoint union type, denoted by the name of an enum item. [^enumtype]
r[type.enum.declaration] 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.
r[type.enum.constructor] New instances of an enum can be constructed with a struct expression.
r[type.enum.value] 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.
r[type.enum.name] 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 Haskell, or a pick ADT in Limbo.