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Type narrowing for Tuple-Elements #12849
Description
TypeScript Version: nightly (2.2.0-dev.20161210)
Code
function test([a, b]: [number, number] | [string, string]) {
if (typeof a === 'number') {
b++
}
}Expected behavior:
b to be narrowed to number and the resulting code to throw no compiler errors
Actual behavior:
b has type number | string and thus the code throws a compiler error complaining that b++ can only apply to numbers
Activity
mhegazy commentedon May 5, 2017
Same underlying issue as #14957
christyharagan commentedon May 6, 2017
Should I close this in favour of #14957 ?
mhegazy commentedon May 8, 2017
I would leave them both open. though both would be addressed by the same change, ppl tend to think of them as two separate scenarios. this way we have a landing point for users searching for similar issues.
RyanCavanaugh commentedon Jul 22, 2020
This would work if it weren't for the destructuring. Our CFA algorithm isn't able to correlate values from different places like this; this comes up from time to time but doesn't seem to merit the required work at this time.