typescript interface syntax for prototyping multidimensional array?

Question

I am trying to add some extension methods for a 2 dimensional array using typescript.

For a 1 dimensional Array the syntax is easy: e.g.

interface Array<T> {
    randomize();  
}
Array.prototype.randomize = function () {
    this.sort(() => (Math.round(Math.random()) - 0.5));
}

I was hoping I could do something similar with a 2 dimensional array, but the following does not work:

interface Array<Array<T>> {
    test();
}

Is it possible in Typescript to prototye on a 2 dimensional array?

Answer 1

There isn't any type system mechanism for this. Fundamentally, at runtime, Array.prototype either has a randomize function or it doesn't. You could write a standalone function that had a constraint, though:

function flatten<T extends Array<any>>(arr: T[]): T {
    return null; // TODO implement
}

var x: string[][] = /* ... */;
var y = flatten(x); // y: string[]
var z = flatten(y); // error

---

As an aside, you should not use that randomize function in earnest. Many sorting algorithms depend on transitivity of ordering (A > B, B > C implies A > C) or stability (A > B implies A > B), which your function does not preserve. This is at best going to be non-uniform and at worst might crash some runtimes.