TypeScript map with generic abstract object

Question

I have several Items that they all inherit from the abstract Item. The object should contain a map with different Item implementations. With my current code I encountered the following error in the Object:

TS2314: Generic type 'Item<'T'>' requires 1 type argument(s)

In Java, that's not a problem. How do I get this to work in TypeScript?

Items

abstract class Item<T> {

}


class Item1 extends Item<boolean> {

}


class Item2 extends Item<number> {

}

Object.ts

class Object {
    private itemMap: Map<number, Item>;
}

Istvan Szasz · Accepted Answer · 2019-10-14 21:34:44Z

2

Try this:

class Object {
    private itemMap: Map<number, Item1 | Item2>;
}

If you plan to add new classes extending Item and support those in Object, you could use Item<any>.

It would work for all the generic types for which a derived Item class exists; and you couldn't instantiate objects with generic types for which you haven't declared a derived class:

class Object {
  private itemMap: Map<number, Item<any>>;

  public constructor() {
    this.itemMap = new Map();
    this.itemMap.set(1, new Item1());         // ok
    this.itemMap.set(2, new Item2());         // ok
    this.itemMap.set(3, new Item<string>());  // Error: Cannot create an instance of an abstract class.
  }
}

edited Oct 14, 2019 at 21:34

answered Oct 14, 2019 at 15:57

Istvan Szasz

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1 Comment

laprof Over a year ago

I'll try this later, but it seems to be not clean, because if I create new item classes, there are multiple spots where I have to change code.

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