10 replies

Understanding the "FilterIn" Type in Unify.ts

Probably a beginner's question:
I am slowly diving into the depths of Effect and in Unify.ts, I saw this:

type FilterIn<A> = A extends any ? typeSymbol extends keyof A ? A : never : never

type FilterIn<A> = A extends any ? typeSymbol extends keyof A ? A : never : never

type FilterIn<A> = A extends any ? typeSymbol extends keyof A ? A : never : never

type FilterIn<A> = A extends any ? typeSymbol extends keyof A ? A : never : never

I have been scratching my head for 2 days, have read and reread Typescript's docs. I still can't figure out when

A extends any

A extends any

A extends any

A extends anycould not be true?