Typing

Typing Basis

With Reified generic types, type parameters are taken into account, respecting the typing semantics as much as possible.

Python's native isinstance function works seamlessly with reified generic types.

In the context of reified generics:

>>> isinstance(ReifiedList[int](), ReifiedList[int])
True

The above expression returns True as a ReifiedList object of integer type is indeed an instance of a ReifiedList of integer type.

On the other hand:

>>> isinstance(ReifiedList[str](), ReifiedList[int])
False

This returns False because, while both objects are instances of the ReifiedList class, their type parameters are different (string vs integer).

Type Equivalence

It treats two instances of the same Reified-derived class as equivalent only if the type parameters provided in their instantiation are exactly the same. That is, ReifiedClass[T, ...] == ReifiedClass[S, ...] if and only if (T, ...) == (S, ...).

>>> ReifiedList[float] == ReifiedList[float]
True
>>> ReifiedList[float] == ReifiedList[int]
False
>>> ReifiedList[tuple[int, str]] == ReifiedList[tuple[int, str]]
True
>>> ReifiedList[tuple[int, str]] == ReifiedList[tuple[int, float]]
False
>>> ReifiedList[ReifiedList[int]] == ReifiedList[ReifiedList[int]]
True
>>> ReifiedList[ReifiedList[int]] == ReifiedList[ReifiedList[str]]
False

Subtyping

The Reified Mixin supports nominal subtyping.

Let types A and B be Reified-derived classes. Type A is a subtype of type B if A == B or A is directly derived from B.

A Reified derived class with type parameters is considered a subtype of the same class without type parameters. This means that ReifiedClass[T, ...] is a subtype of ReifiedClass.

>>> issubclass(ReifiedList[int], ReifiedList[int])
True
>>> issubclass(ReifiedList, ReifiedList[int])
False
>>> issubclass(ReifiedList[int], ReifiedList)
True
>>> issubclass(ReifiedList[str], ReifiedList[int])
False
>>> class ReifiedListSub(ReifiedList[int]):
...     pass
...
>>> issubclass(ReifiedListSub, ReifiedList[int])
True

Type Variance

The Reified Mixin only considers direct equivalence of type parameters for subtyping and does not account for type variance.

>>> issubclass(bool, int)
True
>>> class ReifiedTuple[T](Reified, tuple[T]):
...     pass
...
>>> issubclass(ReifiedTuple[bool], ReifiedTuple[int])
False