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- from collections.abc import Callable
- from typing import Generic, TypeVar
- R = TypeVar("R")
- class Thunk(Generic[R]):
- """
- A simple lazy evaluation implementation that lets you delay
- execution of a function. It properly handles releasing the
- function once it is forced.
- """
- f: Callable[[], R] | None
- r: R | None
- __slots__ = ["f", "r"]
- def __init__(self, f: Callable[[], R]) -> None:
- self.f = f
- self.r = None
- def force(self) -> R:
- if self.f is None:
- return self.r # type: ignore[return-value]
- self.r = self.f()
- self.f = None
- return self.r
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