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Can't extend mixin constructor that constructs a generic type

See original GitHub issue

This applies regardless of whether or not I intersect it with some bogus type, or have a reasonable constraint. So none of the following works.

Returning a plain T

export type Constructor<T> = new (...args: any[]) => T

export interface Timestamp {
    timestamp: Date;
}

// plain old T
export function Timestamp<T, CT extends Constructor<T>>(Base: CT): Constructor<Timestamp> & Constructor<T> {
    return class extends Base {
        timestamp = new Date();
    }
}

Constructor of T with a bogus object type ({})

export type Constructor<T> = new (...args: any[]) => T

export interface Timestamp {
    timestamp: Date;
}

// Constructor of T with a bogus object type
export function Timestamp<T, CT extends Constructor<T & {}>>(Base: CT): Constructor<Timestamp> & Constructor<T> {
    return class extends Base {
        timestamp = new Date();
    }
}

Constructor of T where T is constrained to {}

export type Constructor<T> = new (...args: any[]) => T

export interface Timestamp {
    timestamp: Date;
}

export function Timestamp<T extends {}, CT extends Constructor<T>>(Base: CT): Constructor<Timestamp> & Constructor<T> {
    return class extends Base {
        timestamp = new Date();
    }
}

Constructor of T where T is constrained to object (see also #13805)

export type Constructor<T> = new (...args: any[]) => T

export interface Timestamp {
    timestamp: Date;
}

export function Timestamp<T extends object, CT extends Constructor<T>>(Base: CT): Constructor<Timestamp> & Constructor<T> {
    return class extends Base {
        timestamp = new Date();
    }
}

Issue Analytics

State:
Created 7 years ago
Reactions:10
Comments:6 (2 by maintainers)

Top GitHub Comments

6reactions

alber70gcommented, Feb 4, 2019

Anything to say about this? Is there a workaround possible? I’m anxious to hear about this, since we need it.

Another option could be that this is not proper coding, then I’d like to hear about it, as well.

0reactions

alber70gcommented, Jan 28, 2019

Any resolution on this?

I’m trying to do something similar where I want to use a class-mixin in another class-mixin.

A small example here:

class MyClass {
  myClass = 1;
}
type Constructor<T extends MyClass> = new (...args: any[]) => T;

function make1<T extends Constructor<MyClass>>(base: T) {
  return class extends base {
    make1 = 1;
  };
}
/**
 * [ts] Type '{
 *   new (...args: any[]): make3<T>.(Anonymous class);
 *   prototype: make3<any>.(Anonymous class); } & T'
 * is not a constructor function type. [2507]
 */
function make2<T extends Constructor<MyClass>>(base: T) {
  return class extends make1(base) {
    make2 = 2;
  };
}

class Test extends MyClass {}

class Test2 extends make2(Test) {
  constructor() {
    super();
    // this.myClass is gone
    // this.make1 is gone
    // only this.test2 exists
  }
}