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