Exhaustive match (RFC 40) #1891
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jemc
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I'm submitting this for review/merge with a couple of caveats:
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Looks like there's a legitimate issue in the CI that needs to be fixed before merging. |
Construct a union type of all cases in the match that match on type alone, and if this union is a supertype of the match expression type, then the match is exhaustive so we don't need to sugar the `else None`. As a result, users won't have to deal with the type system possibility of a `None` result for match blocks which can easily be shown to never reach the `else` case.
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Alright, rebased on top of latest master and fixed the issue. Expecting CI to pass this time. |
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One of the Travis builds had a blip downloading LLVM - restarted that particular build. |
SeanTAllen
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May 10, 2017
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This PR implements RFC 40.
Construct a union type of all cases in the match that match on type alone,
and if this union is a supertype of the match expression type,
then the match is exhaustive so we don't need to sugar the
else None.As a result, users won't have to deal with the type system possibility of a
Noneresult for match blocks which can easily be shown to never reach the
elsecase.Closes #1772.