Fix & improve match & add matchTag#8
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LukasKalbertodt
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Unfortunately, `match` had a problem where sometimes it was unsound.
This was not really the fault of `match` as TS has questionable
semantics regarding `Record<string, _>`. The following worked before:
const foo: number = match("bla", {
"a": () => 3,
});
So: no fallback, an incomplete object and still, it returns `number`.
This can of course fail at runtime. The problem is that `Record<X, _>`
works differently for `string` and for unions of strings.
The new version solves this by returning `Out | null` if not all cases
are covered, meaning that for `string` it always returns `Out | null`.
I also removed the `fallback` overload as the same can easily be
achieved via `?? fallback`.
I also added a rudimentary compile-test to make sure the problematic
cases actually cause compile errors.
LukasKalbertodt
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Unfortunately
matchwas unsound before and could allow getting variables of typeTwhen it should have beenT | null. See the relevant commit message for more information. The changes tomatchare breaking, so this requires a major version bump.