Array.concat() 's params wrong!!!

[scp1513]

TypeScript Version: 2.4.1

Code

let a: ReadonlyArray<number> = [];
let b: number[] = [];
// compile error
let c = b.concat(a);
// you see Array.concat() doesn't change the params

Expected behavior:

Actual behavior:

[MrKou47]

let a: ReadonlyArray<number> = [];
let b: number[] = [];
let c = b.concat([...a]);

this will be ok.

[scp1513]

@MrKou47 It works. thanks.

[arusakov]

@RyanCavanaugh
Code example generates error (TypeScript 2.5.2):

[ts]
Argument of type 'ReadonlyArray<number>' is not assignable to parameter of type 'number | number[]'.
  Type 'ReadonlyArray<number>' is not assignable to type 'number[]'.
    Property 'push' is missing in type 'ReadonlyArray<number>'.

Is it right definition for push method for ReadonlyArray<T>?

push(): never

Also we need the same definitions for other methods, like pop and so on... Am I right?

[mhegazy]

PRs welcomed. You can find more information about contributing lib.d.ts fixes at https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md#contributing-libdts-fixes.

[NaridaL]

This is a duplicate of #17076 and has been fixed by #17806.