Generator expects key type K of int|string, K of int|string given.

[RikudouSage]

Bug report

Generator expects key type K of int|string, K of int|string given.

Code snippet that reproduces the problem

https://phpstan.org/r/11599e77-4519-411d-b01f-77a89226a09c

Expected output

No error.

[rvanvelzen]

The error message is ambiguously formatted, but it is correct. This is what it's actually saying: Generator expects key type (K of int)|string, K of int|string given..

Parenthesization should be improved.

[ondrejmirtes]

Somewhere here: https://github.com/phpstan/phpstan-src/blob/82dfce133e9c9baf7f1fb05b64a60a8e6b4c2dd9/src/Type/UnionType.php#L207-L218

[RikudouSage]

@rvanvelzen Doesn't it boil down to expecting int or a string? Which I'm providing?

[rvanvelzen]

You're not yielding a key of K because you're changing the type if it's a string. You can resolve it by using a conditional type: https://phpstan.org/r/e466fec7-aa7b-45e0-9c94-1c3503da9a00

[RikudouSage]

That doesn't make sense to me... I'm saying that it returns int or string and that it's the same as what the original array has. Strtoupper and strtolower don't change string into something else, they return string.

[rvanvelzen]

strtolower and strtoupper change K to string, which is not the same as K.

One way of looking at it is that K refers to the value, so if you modify the value the type does not remain K.

[RikudouSage]

I understand what you're saying, it just doesn't make sense to me. That function basically accepts iterable<int|string, mixed> and returns iterable<int|string, mixed>.

I used the template only for the added benefit of knowing that if you provide int keys you get int keys back. K is a type, not a value and the type returned is correct.

[ondrejmirtes]

Yes, that's why you need a conditional return type and not generics.

[github-actions]

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