Exploring the representation of recursive types using generic type constraints

Is there a way to create a structure that can handle recursive relationships like the one described below? I am looking to limit the types of values that can be added to a general container to either primitive data types or other containers. Due to limitations with interfaces not being able to extend from types and types not being able to reference themselves, it is uncertain whether this can be achieved:

  type Primitive = string | boolean | number | null;
  type Value = Primitive | MyContainer<Value>;  // <-- error here


  interface MyContainer<T extends Value> {
    get(key: string): T;
    set(key: string, value: T): void;
  }
typescript

Answer №1

In programming, types have the ability to reference themselves in certain scenarios (as described in the spec), but this can lead to potential pitfalls. For a specific case like yours, it is advisable to define types in a clear and concise manner:

type Primitive = string | boolean | number | null;

type Value = Primitive | MyMap; 

interface MyMap {
  get(k: string): Value;
  set(k: string, v: Value): void;
}

Avoid introducing unnecessary generics that could complicate the structure.

Update 1

In response to @Chris Colbert's comment on the use of generics for recursive types:

The generic plays a crucial role as it allows for operations such as: 

let m1: MyMap<string>; let m2: MyMap<MyMap<number>>;
and so forth.

For this requirement, consider the following approach:

type Primitive = string | boolean | number | null;

type Value = Primitive | {
  get(k: string): Value;
  set(k: string, v: Value): void;
}

interface MyMap<T extends Value> {
  get(k: string): T;
  set(k: string, v: T): void;
}

declare let m1: MyMap<string>; 
declare let m2: MyMap<MyMap<number>>;

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