What is a recursive type?
- TypeScript course
- Advanced
- Lesson 9/57
- 4 min
Learn self-referencing types.
What is a recursive type?
A recursive type is a type that references itself in its definition. Linked lists, trees, and nested structures are defined this way. A field points to a value of the same type; this allows modeling data of unlimited depth. The chain can be terminated by making the field optional (?).
type LinkedList<T> = {
value: T;
next?: LinkedList<T>;
};Termination with optional fields
In recursive types, the self-referencing field is made optional (?); this lets the chain end at some point. For example, in next?: LinkedList<T>, if next is absent the list ends. This allows modeling finite data without falling into infinite recursion.
Practice Create a linked list object
Define a recursive generic type named BagliListe: <T> = { deger: T; sonraki?: BagliListe<T> }. The liste variable should be of type BagliListe<number> with value { deger: 1, sonraki: { deger: 2 } }. Print liste.deger with console.log.
Starter code
// BagliListe adinda recursive generic type tanimla
// deger ve opsiyonel sonraki alanlari olsun
// liste nesnesini number degerlerle tanimla
// liste.deger yazdirSample solution
type BagliListe<T> = {
deger: T;
sonraki?: BagliListe<T>;
};
const liste: BagliListe<number> = { deger: 1, sonraki: { deger: 2 } };
console.log(liste.deger);Expected output
1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the defining feature of a recursive type?
- It contains only primitive types
- It changes at runtime
- It cannot take generic parameters
- It references itself in its definition Correct answer
Explanation: A recursive type references its own name in its definition; this allows modeling nested data of unlimited depth.
2 Self-reference
type BagliListe<T> = {
deger: T;
sonraki?: ____<T>;
};type BagliListe<T> = {
deger: T;
sonraki?: BagliListe<T>;
};Explanation: A recursive type references itself; the next field must also be of type BagliListe<T>.
3 Recursive type concepts
| Term | Meaning |
|---|---|
deger |
Node value |
sonraki? |
Optional next node |
BagliListe<T> |
Self-referencing type |
T |
Type of node value |