TS won't complain comparing a key value

[sinful garden]

ricmed#0

Playground Link

Preview:ts class Mods { a?: true ...

[golden gate]

!:unsafe-keys

[sinful garden]

retsam19#0

`!retsam19:unsafe-keys`:

Since TS allows objects to have extra properties not specified in the type, it doesn't assume that all the keys on the type are the only keys on the object. This means that Object.keys returns string[] not a specific type, and for(const key in obj), key is string, (not keyof typeof obj).

If you wish to assume otherwise, this utility is often helpful:

// A signature for `Object.keys` that assumes the only keys are the ones indicated by the type
const unsafeKeys = Object.keys as <T>(obj: T) => Array<keyof T>;

[golden gate]

besides that, you've explicitly said that you allow excess keys by saying M extends Mods

Extract<keyof M, string> is not "a" | "b", that's Extract<keyof Mods, string>
M might have more keys

[harsh steppe]

Got it. Shouldn't it be called "safeKeys" though?

Would want to avoid the slower Object.keys() path, is it a good idea to do this? (also, can I cast the key right in the for in line?)
https://www.typescriptlang.org/play?strict=false&strictPropertyInitialization=false&noImplicitThis=false&noImplicitReturns=false&ssl=1&ssc=1&pln=2&pc=1#code/MYGwhgzhAECyD2ATGBvAUASDAfgFzQBcAnAVwFNMAjPQ0igXzSYDMSA7YAgS3jemYCMACgC2A-AmQAaaCIBMEpBACU0dBmbwi0ISDIFoAa2hc+Y1eozBeEAwCtoAXh3HIRsgE94zOEujLMDC4fIQdHcOgAImsRAAdwUwgAcXgkSItAjEDGDAwAejyTEIBCIWNTWTllDNyC6Ax5AG1DAF0nWQFmlsC6nMZGNCA

[sinful garden]

@harsh steppe Here's a shortened URL of your playground link! You can remove the full link from your message.

ricmed#0

Playground Link

Preview:ts class Mods { a?: true ...

[golden gate]

well no, it's explicitly unsafe
i don't mean to use that snippet, but the explanation there is relevant

[golden gate]

if it's not thousands of properties, then speed probably shouldn't be a concern

[golden gate]

casting is never really a good idea. with the function as it is, you can't be sure that k is actually a keyof Mods unless you're completely confident about how you call it

[harsh steppe]

" unless you're completely confident about how you call it" I can

can I cast the key right in the for in line?

[golden gate]

that it's always going to be in that shape?

[golden gate]

no, that syntax isn't allowed

[harsh steppe]

I guess so, it's an internal class

I think const j = (k as keyof typeof param1) is better

[golden gate]

that doesn't change anything

why do you need to iterate over the keys of an internal class anyways?

key iteration would generally be used for records or unknown structures

since it's basically reflection

[harsh steppe]

you're right

thanks!