Inheriting from multiple base classes clarification

[lindi0v]

First of all, polytype is awesome!

Not sure if I'm facing a bug or just don't understand something. It's about accessing base classes properties. Docs says: If different base classes include a member with the same name, the syntax super.class(DirectBaseClass).member can be used to make the member access unambiguous.

Now, I have situation like this:

import { classes } from 'polytype';

const getId = () => {
  return String(Math.random().toFixed(3).replace('.', ''));
};

class WithId {
  id = getId();

  constructor() {
    console.log(111, 'WithId id', this.id);
  }
}

class A extends classes(WithId) {
  constructor() {
    super();
    console.log(111, 'A id', this.id);
  }
}

class B extends classes(WithId) {
  constructor() {
    super();
    console.log(111, 'B id', this.id);
  }
}

class C extends classes(A, B) {
  constructor() {
    super();
    console.log(111, 'C id', super.class(A).id, this.class(A).id, this.id);
  }
}

const c = new C();

I expect that super.class(A).id or this.class(A).id will be equal to A.id, but they are undefined. Why does this happen? I set up an example on stackblitz: https://stackblitz.com/edit/vitejs-vite-rbg1gv?file=src%2Fmain.ts

[fasttime]

Hi @lindi0v, thanks for the appreciation. The behavior you observe is expected since the super keyword can only access properties on an object's prototype, but in your case, the id property is always set on the new object itself with id = getId();.

You can compare your code to the simplified example below, where class C inherits directly from WidthId, without using Polytype.

const getId = () => {
  return String(Math.random().toFixed(3).replace('.', ''));
};

class WithId {
    id = getId();
  
    constructor() {
      console.log('WithId id', this.id);
    }
}

class C extends WithId {
  constructor() {
    super();
    console.log('C id', super.id, this.id);
  }
}

const c = new C();

When I run this locally, it prints something like:

WithId id 0107
C id undefined 0107

Note in the last line that super.id is undefined, exactly like super.class(A).id or this.class(A).id in your code (those are equivalent).

[lindi0v]

got it, thanks!