Fix intersections #129
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Fix intersections #129
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In typescript 3.9.0, the intersection between two objects will be `never` if the two objects have incompatible private members. This broke an implicit behavior that `CombineObjects` was taking advantage of; element-wise intersection. Because `CombineObjects` is intended to be a thin wrapper over the raw intersection type, I don't want its contract to deviate from the intersection. So instead I added the `ElementwiseIntersect` utility; which relies on the newly added `TryKey` utility. `TryKey` is just like `GetKey`, except it fails "silently" when the key does not exist. Specifically, `GetKey` returns `never` so that the resultant type is unusable and `TryKey` returns `unknown` which can be eliminated via intersection. Relevant PR from typescript which changed behavior of intersections (and broke the future-proofing test cases): microsoft/TypeScript#37762
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In typescript 3.9.0, the intersection between two objects will be
neverif the two objects have incompatible private members. This brokean implicit behavior that
CombineObjectswas taking advantage of;element-wise intersection. Because
CombineObjectsis intended to be athin wrapper over the raw intersection type, I don't want its contract
to deviate from the intersection. So instead I added the
ElementwiseIntersectutility; which relies on the newly addedTryKeyutility.
TryKeyis just likeGetKey, except it fails "silently" when the keydoes not exist. Specifically,
GetKeyreturnsneverso that theresultant type is unusable and
TryKeyreturnsunknownwhich can beeliminated via intersection.
Relevant PR from typescript which changed behavior of intersections (and
broke the future-proofing test cases):
microsoft/TypeScript#37762