Improve `Array.from(tuple)` and `[...tuple]`

Suggestion

Array.from(tuple) and [...tuple] should preserve individual types that made up tuple.

Proposal

Array.from (Simple)

Add this overload to Array.from:

interface ArrayConstructor {
  from<T extends any[]> (array: T): T
}

demo 1

Caveats:

• The above definition preserves everything including unrelated properties that do not belong to Array.prototype whilst actual Array.from discards them. (for instance, if input has foo: 'bar', output array will also has foo: 'bar').

Array.from (Complete)

Fix above caveats.

interface ArrayConstructor {
  from<T extends any[]> (array: T): CloneArray<T>
}

type CloneArray<T extends any[]> = {
  [i in number & keyof T]: T[i]
} & {
  length: T['length']
} & any[]

demo 2

Spread operator

declare const tuple: [0, 1, 2] & { foo: 'bar' }

// $ExpectType [string, string, 0, 1, 2, string, string]
const clone = ['a', 'b', ...tuple, 'c', 'd']

Note that typeof clone does not contain { foo: 'bar' }.

Use Cases

• Clone a tuple without losing type information.

Examples

Clone a tuple

const a: [0, 1, 2] = [0, 1, 2]

// $ExpectType [0, 1, 2]
const b = Array.from(a)

Clone a generic tuple

function clone<T extends any[]> (a: T): T {
  return Array.from(a)
}

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

Como el issue no menciona archivos del repositorio, pruebas ni puntos de entrada, comienza leyendo las propuestas sobre Array.from y spread y sus ejemplos vinculados. Se considera terminado cuando, para los casos descritos de Array.from y spread, se conservan los tipos de los elementos y de la longitud de las tuplas sin cambiar el comportamiento en tiempo de ejecución de JavaScript.