与通用接口一起使用时，Typescript 无法正确推断类型

Question

Here is my code :

import {FieldType} from '/imports/common/core/schema/Schema';

interface Content<S, F extends keyof S> {
  name: F
  type: FieldType | Container<S[F]>
}

class Container<S> {
  content: Content<S, keyof S>;

  constructor(content: Content<S, keyof S>) {
    this.content = content;
  }
}

type Parent = {
  height: number
};

type Child = {
  age: number
  parent: Parent
}

const containerParent = new Container<Parent>({
  name: 'height',
  type: FieldType.String
});

new Container<Child>({
  name: 'parent',
  type: containerParent // This line fails....
});

You can try it here :

Exemple

I want to know how I could make TS to infer that the value I want the "type" property to expect to receive a Container, because I set the name to 'parent' the line before. For now it waits for a Container<number | Parent>...

Edit:

Updated exemple

Answer 1

The problem is that Content is based on a specific key of S , but Container uses all keys of S for its type instead of any specific key. So the type of the constructor argument is expected to be string | Container<S[keyof S]> string | Container<S[keyof S]> .

The errors go away if you change Container to take a second generic for the key. You can make that second variable optional and have default to keyof S so that you don't need to change Container<Parent> .

class Container<S, F extends keyof S = keyof S> {
  content: Content<S, F>;

  constructor(content: Content<S, F>) {
    this.content = content;
  }
}

With the current setup, you do have to set the key generic on the child container for it to work. You can't tell typescript to infer the second type while explicitly setting the first.

new Container<Child, 'parent'>({
  name: 'parent',
  type: containerParent
});

Playground Link