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Array/Observable filter does not infer chained type #19640
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I noticed this by a different case actually, probably should have posted that one.
['foo', 'bar', null] .filter(Boolean) .map(s => s.toUpperCase());
This worked with TS ~2.3 and is not working anymore with TS ~2.6. I thought the above would be a simpler reproduction but it seems it is something completely different :) Thanks for your hint though, this helps but still required quite a few new guards in our codebase which worked in a previous TS version 😕
You're right doesn't work on arrays, we do have some rxjs observables where this works though, no idea what exactly is different there or if it's project specific.. I will report back later this week.
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.
Not sure why this not working:
const list: (string | null)[] = ['A', null, 'C'] list.filter<string>((_) => _ !== null).map(x => x.)
Tried latest dev 2.7 still not working and not inferring
A user-defined type guard is not inferred automatically, a type annotation is expected. i.e.:
const list: (string | null)[] = ['A', null, 'C'] function isNotNull<T>(a: T | null): a is T { return a !== null; } list.filter(isNotNull).map(x => x.)
Reacted by Zack Ream, Alexander von Weiss and Vlad SabevA user-defined type guard is not inferred automatically, a type annotation is expected. i.e.:
It is good to hear, but still complicated, not clear whey it not possible to have auto inference here.
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on Jul 3, 2018
TypeScript Version: 2.6.1 using
strict: trueCode
Expected behavior:
Compiles
Actual behavior: