Examples

Example Usage 1: Type-Checked Generic Stack

from reification import Reified


class ReifiedStack[T](Reified):
    def __init__(self) -> None:
        super().__init__()
        self.items: list[T] = []

    def push(self, item: T) -> None:
        # We can do runtime check
        if isinstance(item, self.targ):
            self.items.append(item)
        else:
            raise TypeError()

    def pop(self) -> T:
        if self.items:
            return self.items.pop()
        else:
            raise IndexError("pop from empty stack")


stack = ReifiedStack[str]()
stack.push("spam")  # OK
stack.push(42)  # raises TypeError

The ReifiedStack class created here is generic and derived from the Reified base class, and implements a simple stack with push and pop methods.

In the push method, we are checking at runtime if the item being pushed is of the specified generic type (this type is accessible via the targ attribute inherited from Reified). If the type of the item does not match, a TypeError is raised.

In the example usage, we create an instance of the ReifiedStack class with str as the type argument. When we try to push a string "spam", the item is accepted since it matches the stack's specified type argument. However, when we try to push an integer 42, a TypeError is raised because the type of the item does not match the stack's type argument.

This demonstrates the use of reified generics in Python where we can have runtime access to the type parameters, enabling us to type check dynamically at runtime. This is useful in situations where we need to enforce type safety in our code or use type information at runtime.

Example Usage 2: Multi-Parameter Typed Registry

from reification import Reified


class TypedRegistry[K, V](Reified):
    def __init__(self) -> None:
        super().__init__()
        self._store: dict[K, V] = {}

    def register(self, key: K, value: V) -> None:
        key_type, value_type = self.type_args
        if not isinstance(key, key_type):
            raise TypeError(f"Key must be {key_type.__name__}, got {type(key).__name__}")
        if not isinstance(value, value_type):
            raise TypeError(f"Value must be {value_type.__name__}, got {type(value).__name__}")
        self._store[key] = value

    def lookup(self, key: K) -> V:
        return self._store[key]

    def entries(self) -> list[tuple[K, V]]:
        return list(self._store.items())


registry = TypedRegistry[str, int]()
registry.register("apples", 3)   # OK
registry.register("bananas", 5)  # OK
registry.register(42, "spam")    # raises TypeError (key must be str)

This example demonstrates the use of multiple type parameters with type_args.