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Expressive Reversed type for tuples #60575
Description
⚙ Compilation target
ES2024
⚙ Library
5.6.3
Missing / Incorrect Definition
interface Array<T> {
reverse: T[];
}This loses all information of the order of reversed tuples, I usually have to use the following code to override the behaviour of Array.prototype.reverse
type ReversedTuple<T extends any[], R extends any[] = []> = ReturnType<T extends [infer F, ...infer L] ? () => Reverse<L, [F, ...R]> : () => R>;
type ReversedTupleOrArray<T> = T extends [any, ...any[]] ? Reverse<T> : T;Sample Code
const myTuple: [number, string, string] = [1, 'hello', 'world']
const reversedTuple = myTuple.reverse() // (string | number)[]
Activity
MartinJohns commentedon Nov 24, 2024
Related: #13360 (comment)
And in general
reverse()is troublesome for tuples, because it modifies the array in-place.redpulp commentedon Nov 24, 2024
Yeah tuples should be immutable by definition, so I get how this would be troublesome here. I only know of dirty tricks to avoid this (like
[...array].reverse()) so I understand the issue, thanks for the comment