Recursive generic types

Learn self-referencing generic types.

What is a recursive generic type?

A recursive generic type is a type that references itself in its definition. For example, tree structure types are defined this way. The expression type Tree<T> = { value: T; left?: Tree<T>; right?: Tree<T> } references the same type within itself.

type Tree<T> = {
  value: T;
  left?: Tree<T>;
  right?: Tree<T>;
};

Deep access with recursive types

A recursive generic type provides type-safe access to deeply nested data. Each node carries its own value and child nodes of the same type. The left and right fields are optional; leaf nodes may have no children.

const leaf: Tree<number> = { value: 5 };
const branch: Tree<number> = {
  value: 3,
  left: { value: 1 }
};

Exercise Create a tree object

Define a recursive generic type named Agac: <T> = { deger: T; sol?: Agac<T>; sag?: Agac<T> }. The kok variable should be of type Agac<number> with value { deger: 1, sol: { deger: 2 } }. Print kok.sol.deger with console.log.

Show example solution

type Agac<T> = {
  deger: T;
  sol?: Agac<T>;
  sag?: Agac<T>;
};
const kok: Agac<number> = { deger: 1, sol: { deger: 2 } };
console.log(kok.sol.deger);

Test yourself

Where is a recursive generic type typically used?
- For single-valued numbers
- Only for strings
- For self-repeating structures like trees or lists
- For fixed-length arrays
Show answer

For self-repeating structures like trees or lists — A recursive generic type is used to define self-repeating nested structures such as trees and linked lists.

Recursive generic parameter

type Agac<T> = {
  deger: T;
  sol?: ____<T>;
  sag?: Agac<T>;
};

Show answer

type Agac<T> = {
  deger: T;
  sol?: Agac<T>;
  sag?: Agac<T>;
};

Recursive generic concepts

Agac<T>

Self-referencing type
deger

Node value
sol?

Optional left subtree
sag?

Optional right subtree

Next lesson: Summary - Advanced generics

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