factory

discopy.cat.factory(cls)

Allows the identity and composition of an Arrow subclass to remain within the subclass, by setting cls.factory = cls.

Parameters:

cls – Some subclass of Arrow.

Note

The factory method pattern (FMP) is used all over DisCoPy. For backward compatibility, the factory is also available as the class property cls.ar, see discopy.abc.Category.

Example

Let’s create Circuit as a subclass of Arrow with an Ob subclass Qubit as domain and codomain.

>>> from discopy.cat import Ob, Arrow, Box
>>> class Qubit(Ob):
...     pass
>>> @factory
... class Circuit(Arrow):
...     ob = Qubit

The Circuit subclass itself has a subclass Gate as boxes.

>>> class Gate(Box, Circuit):
...     pass

The identity and composition of Circuit is again a Circuit.

>>> X = Gate('X', Qubit(), Qubit())
>>> assert isinstance(X >> X, Circuit)
>>> assert isinstance(Circuit.id(), Circuit)
>>> assert isinstance(Circuit.id().dom, Qubit)
>>> assert Circuit.factory is Circuit.ar is Circuit