Summary - Advanced generics

Write a concat helper with variadic tuples.

Summary - Advanced generics

In this group you learned advanced generic topics: variadic tuples provide variable-length type-safe tuples; tuple inference derives the tuple type from call arguments in generic functions; recursive generic types define self-referencing nested structures. Together they enable powerful, type-safe abstractions.

type Headed<T> = [string, ...T[]];
type Tree<T> = { value: T; left?: Tree<T> };

Exercise Write a concat helper

Define a generic type named Birlestir: <A extends unknown[], B extends unknown[]> = [...A, ...B]. Define function birlestir<A extends unknown[], B extends unknown[]>(a: A, b: B): Birlestir<A, B> whose body returns return [...a, ...b]. Assign the result of calling birlestir([1, 2], ["a", "b"]) to sonuc and print sonuc[2] with console.log.

Show example solution

type Birlestir<A extends unknown[], B extends unknown[]> = [...A, ...B];
function birlestir<A extends unknown[], B extends unknown[]>(a: A, b: B): Birlestir<A, B> {
  return [...a, ...b];
}
const sonuc = birlestir([1, 2], ["a", "b"]);
console.log(sonuc[2]);

Test yourself

Which of the following is an example of a variadic tuple?
- [string, ...number[]]
- number[]
- { a: number }
- [number, string]
Show answer

[string, ...number[]] — A variadic tuple is a tuple containing the spread operator; [string, ...number[]] is an example with a fixed head and a variable-length tail.

Recursive type self-reference

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

Show answer

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

Advanced generics summary

variadic tuple

Variable-length tuple
tuple inference

Tuple from call
recursive type

Self-referencing type
...T[]

Spread tuple

Next lesson: What is a template literal?

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