types-kit.flat.md

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Flat type

Create an array that includes the flatten array type.

Signature:

export type Flat<T extends readonly unknown[]> = T extends T
  ? true extends IsTuple<T>
    ? T extends readonly [infer A, ...infer B]
      ? A extends readonly unknown[]
        ? IsReadonlyArray<T> extends true
          ? readonly [...Flat<A>, ...Flat<B>]
          : [...Flat<A>, ...Flat<B>]
        : IsReadonlyArray<T> extends true
        ? readonly [A, ...Flat<B>]
        : [A, ...Flat<B>]
      : T extends readonly [...infer A, infer B]
      ? B extends readonly unknown[]
        ? IsReadonlyArray<T> extends true
          ? readonly [...Flat<A>, ...Flat<B>]
          : [...Flat<A>, ...Flat<B>]
        : IsReadonlyArray<T> extends true
        ? readonly [...Flat<A>, B]
        : [...Flat<A>, B]
      : never
    : // array or empty array
    true extends IsEmptyTypeArray<T>
    ? IsReadonlyArray<T> extends true
      ? readonly []
      : []
    : IsReadonlyArray<T> extends true
    ? readonly FlattedArrayItem<T>[]
    : FlattedArrayItem<T>[]
  : never

References: IsTuple, IsReadonlyArray, Flat, IsEmptyTypeArray, FlattedArrayItem

Example

// Expect: [1, 2, 3, 4]
type Foo = Flat<[1, [[2, [3, [4]]]]]>