Ts-toolbelt: Why is `<x> extends infer X ? <y> : never` so used?
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The whole codebase is full of <x> extends infer X ? <y>: never
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extends #infer #lots #used
millsp
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I use this syntax to defer the evaluation of a type... Otherwise TS evaluates all the types in their full depth. This causes performance issues and is irrelevant because we only want to compute when we've received the type parameters. As a result, the ts-toolbelt types load fast.
But it is not the only use case. Like I said above, TS can complain that a type is too deep to compute, then you can force it to compute step by step. So I especially use this on recursive types (which are much deeper because they're recursive).
millsp
on 26 Jun 2019
Can you add an example of real code from this project that does this to this wiki entry? It's hard to understand if/how x and X are related in your pseudocode <x> extends infer X ? <y>: never (or if the x's are even relevant, which I think they aren't)
ekilah
on 25 Oct 2019
You can check this example out
millsp
on 25 Oct 2019
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Most helpful comment
I use this syntax to defer the evaluation of a type... Otherwise TS evaluates all the types in their full depth. This causes performance issues and is irrelevant because we only want to compute when we've received the type parameters. As a result, the ts-toolbelt types load fast.
But it is not the only use case. Like I said above, TS can complain that a type is too deep to compute, then you can force it to compute step by step. So I especially use this on recursive types (which are much deeper because they're recursive).