Comments (7)
Hey!
I found this solution too, but I don't have any compilation error (without adding extends boolean
to the type parameter C). It's normal?
type If<C, T, F> = C extends true ? T : F;
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@AurelienWebnation maybe the type system became smart enough to figure it out? Try on the older versions of TypeScript if you are interested in getting an answer to this.
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Such a solution will be more precise
type If<C extends boolean, T, F> = C extends true
? T
: C extends false
? F
: never;
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@shadaxv I think your C extends false
condition is not necessary because this type parameter is constrained to boolean
. So if C extends true
, in the other case, C
can only extends
false.
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This is correct for cases with a boolean type, but if you send another type and comment it out with // @ts-expect-error
, the returned type will be false
instead of never
, but maybe I'm just over-thinking it and it's not needed
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Hi, using this type IF<T, K, L> = T extends true? K: L;
I don't understand why with null the result is "true"
type fromNull = IF<null, "true", "false">; //true
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Hi, using this type IF<T, K, L> = T extends true? K: L; I don't understand why with null the result is "true" type fromNull = IF<null, "true", "false">; //true
You have something wrong, because the code you showed will return "false"
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