Typescript mixin function inferring from subclass generic type

Question

The following is an example of the problem I am experiencing at the moment. I'm trying to write a mixin that properly infers and reflects the generic type from the subclass of the class provided to the mixin.

abstract class A<T = {}> {
  public abstract init(): T;
}

interface IB {
  something: string;
}

class B extends A<IB> {
  public init(): IB {
    return null;
  }
}

type ConstructorOf<T = {}> = new (...args: any[]) => T;

function ApplyC<T extends ConstructorOf<A>>(base: T) {
  abstract class C extends base {

  }
  return C;
}

class D extends ApplyC(B) {
  constructor() {
    super();
    // this.init()
  }
}

Where I written this.init(), the intellisense is telling me that I have an overload on init(), one is init(): {} and the other is init(): IB, the problem with this is that I don't want there to appear to be an overload, and I just want the IB one to appear.

I need the T in A<T = {}> to be inferred somehow in the mixin and pass it to ConstructorOf<A> from the base: T provided.

Looks like a bug, and I couldn't find an existing report. Do you want to submit a report or shall I? — Matt McCutchen
– Matt McCutchen, Commented Sep 26, 2018 at 23:49
Thanks @MattMcCutchen, have submitted bug here: github.com/Microsoft/TypeScript/issues/27420 — Anupheaus
– Anupheaus, Commented Sep 28, 2018 at 8:46
Does this answer your question? Pass generic parameter in Typescript Mixin — Coderer
– Coderer, Commented Mar 28, 2022 at 12:03

igelbox · Accepted Answer · 2018-10-02 19:30:42Z

0

Do you really need to restrict the ApplyC function to receive only subclasses of A? If no you could replace A with any, e.g.:

    function ApplyC<T extends ConstructorOf<any>>(base: T) {

then D.init() will return just IB and nothing else.

answered Oct 2, 2018 at 19:30

igelbox

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