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feat(array/types): Flat respects non-tuple arrays #103

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merged 2 commits into from
May 31, 2023
Merged

feat(array/types): Flat respects non-tuple arrays #103

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feat(array/types): `Flat` respects non-tuple arrays
pskfyi May 30, 2023
8955901
Merge branch 'main' into flat
AustinArey May 31, 2023
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19 changes: 15 additions & 4 deletions array/types.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -22,11 +22,22 @@ export type Fill<T extends readonly unknown[], Value> = {
* `Array.prototype.flat()`.
*
* @example
* const items: Flat<[1, 2, [3, [4], 5]]> = [1, 2, 3, [4], 5]; */
* type Tup = Flat<[1, 2, [3, [4], 5]]> // [1, 2, 3, [4], 5];
* type Arr = Flat<number[][]> // number[]
* type Arr2D = Flat<number[][]> // number[]
* type Mix = Flat<["A", ["B", "C"][]]> // ["A", ...["B", "C"][]] */
export type Flat<T extends readonly unknown[]> = T extends
readonly [infer Head, ...infer Tail]
? Head extends unknown[] ? [...Head, ...Flat<Tail>]
: [Head, ...Flat<Tail>]
readonly [infer Head, ...infer Tail] // If the first and rest are inferable...
? Head extends unknown[] // ...and the first is an array...
? [...Head, ...Flat<Tail>] // ...spread it then recurse on the rest.
: [Head, ...Flat<Tail>] // Otherwise, keep the first and recurse.
//
: T extends readonly [] ? [] // It T is empty, return an empty array.
//
: T extends Array<infer Item extends unknown> // If T is a non-tuple array...
? Item extends unknown[] // ...and it contains an array...
? [...Item] // ...spread it.
: Item[] // Otherwise, keep it.
: [];

/** Represents an array reversed, analogous to `Array.prototype.reverse()`.
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