Narrow types for certain cases of Array.includes #130
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As discussed in #49 a simple
: searchElement is T
won't do, because the assertion is too strong and produces wrong types, especially in the "opposite" cases (e.g. else blocks).My suggestion is to reenable the type guard only for cases where it is safe: Tuple with well known entries - so only entries that are literals without unions.
For example this is safe, because x is
1 | 2 | 3
if and only if the array contains it:Known problem
There is one remaining problem that I know of, where the type guard would do the wrong thing and I cannot imagine a way to prevent this. But depending on how you look at it, it might be ok, since it seems to me that this is actually due to a wider TypeScript problem (bug?)
If the array itself is a union:
But the same problem arises with other type guards as well:
Playground