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Adds docs about exhaustive literal and enum checks - #10860
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ilevkivskyi
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Jul 22, 2021
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Thanks! Looks good, but I have couple suggestions.
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| PossibleValues = Literal['one', 'two'] | ||
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| def assert_exhaustive(value: NoReturn) -> NoReturn: |
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People actually often call this function assert_never() it can be used is some other cases where people want to check statically some will not be executed.
| return False | ||
| assert_exhaustive(x) # E: Argument 1 to "assert_exhaustive" has incompatible type "Literal['three']"; expected "NoReturn" | ||
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| This technique works with ``Enum`` values as well. |
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I would move the Enum reference to the start, and maybe even make this a default example (while mentioning it also works for literal types with a short example). IMO literal types are more for legacy code, while enums are the future.
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@ilevkivskyi thanks a lot for the review! Fixed 👍 |
ilevkivskyi
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Jul 22, 2021
| return True | ||
| elif x == 'two': | ||
| return False | ||
| assert_never(x) # E: Argument 1 to "assert_exhaustive" has incompatible type "Literal['three']"; expected "NoReturn" |
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The comment still refers to the old name assert_exhaustive
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This feature is not-really known from my experience. I had to explain it several times to other devs.
But, I think that this technique should be widely recognised! It is awesome!
Refs #6366