Union classes
Factor handbook > The language > Objects > Classes

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An object is an instance of a union class if it is an instance of one of its members.
UNION:

define-union-class ( class members -- )


Union classes can be introspected:
class-members ( class -- seq )


The set of union classes is a class:
union-class

union-class? ( object -- ? )


Unions are used to define behavior shared between a fixed set of classes, as well as to conveniently define predicates.

See also
Mixin classes, Maybe classes, Tuple subclassing