Readonly<T> not working

[trusktr]

TypeScript Version: 3.3.0-dev.20181208

Search Terms:

Readonly

Code

const a: Readonly<number[]> = [1,2,3]
a[1] = 4

Expected behavior:

Should not let me write.

Actual behavior:

It does.

Playground Link:

http://www.typescriptlang.org/play/#src=const%20a%3A%20Readonly%3Cnumber%5B%5D%3E%20%3D%20%5B1%2C2%2C3%5D%0Aa%5B1%5D%20%3D%204%0A

Related Issues:

[trusktr]

@weswigham based on your labels, I suppose this is something that never worked the way I was expecting above?

[trusktr]

Ah, I didn't know about ReadonlyArray, that works well:

const a: ReadonlyArray<number[]> = [1,2,3]
a[1] = 4

(playground)

[AlCalzone]

It should be ReadonlyArray<number> btw :)