| from typing import Callable, Generic, Optional, 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: Optional[Callable[[], R]] | |
| r: Optional[R] | |
| __slots__ = ["f", "r"] | |
| def __init__(self, f: Callable[[], R]): | |
| 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 | |