TS2322: Type '(new () => typeof Rectangle)[]' is not assignable to type 'Rectangle[]'

I have a function that stamps copies of classes. It takes a class and returns as many copies of classes as I specified. But the problem is not in the function but in its signature. To create new classes I need a function new and to connect it I did extends { new(): T }. I need it to return an array of classes with their type, but instead it returns (new () => typeof Rectangle)[] and I can’t figure out what the problem is. Here is the code.

class Rectangle {
    w!: number;
    h!: number;
}
class Circle {
    radius!: number;
}


function stampFigures<T extends { new (): T } >(someClass: T, count: number): T[] {
    let a = []
    for (let i = 0; i < count; i++)
        a.push(new someClass());

    return a;
}

let a: Rectangle[] = stampFigures(Rectangle, 10); //here i need Rectangle[] but i got (new () => typeof Rectangle)[]
let b: Circle[] = stampFigures(Circle, 20) //and here

console.log(a)
console.log(b)

>Solution :

You need to infer an instance type of class:

class Rectangle {
  w!: number;
  h!: number;
}
class Circle {
  radius!: number;
}


function stampFigures<
  Klass extends { new(): any }
>(someClass: Klass, count: number) {
  let a: InstanceType<Klass>[] = []
  for (let i = 0; i < count; i++)
    a.push(new someClass());

  return a;
}

let a = stampFigures(Rectangle, 10); //  Rectangle[]
let b = stampFigures(Circle, 20) // Circle[]

console.log(a)
console.log(b)

Playground

YOu can also check my article