In the area of
mathematical logic and
computer science known as
type theory, a
unit type is a
type that allows only one value (and thus can hold no information). The carrier (underlying set) associated with a unit type can be any
singleton set. There is an
isomorphism between any two such sets, so it is customary to talk about
the unit type and ignore the details of its value. One may also regard the unit type as the type of 0-
tuples, i.e. the
product of no types.