Multiple type parameters

Learn to take multiple type parameters.

More than one type parameter

A generic can take more than one type parameter. Types are separated by commas: <T, U>. Each parameter is independent and can be used anywhere in the signature. Order matters; the call must give types in the same order.

function cevir<T, U>(x: T, y: U): [U, T] {
  return [y, x];
}
const r = cevir<number, string>(1, "a");
// r: [string, number]

Key-value structures

Multiple type parameters are especially useful for key-value structures. A Map<K, V> maps a K key to a V value. You can write your own Cift<K, V> class to hold two values of different types together, type-safely.

Exercise Key-value pair

Write a generic class Cift<K, V>. It should have private fields anahtar: K and deger: V; the constructor takes these values and assigns them to the fields. Method al(): [K, V] returns [this.anahtar, this.deger]. Then create a Cift<string, number> instance with "yas" and 25, and print the result of al().

Show example solution

class Cift<K, V> {
  private anahtar: K;
  private deger: V;
  constructor(anahtar: K, deger: V) {
    this.anahtar = anahtar;
    this.deger = deger;
  }
  al(): [K, V] {
    return [this.anahtar, this.deger];
  }
}
const c = new Cift<string, number>("yas", 25);
console.log(c.al());

Test yourself

How is a generic with two type parameters declared?
- Two letters separated by semicolon, inside angle brackets
- Two letters separated by space, inside angle brackets
- Two letters inside angle brackets, separated by comma
- Two letters inside square brackets, separated by comma
Show answer

Two letters inside angle brackets, separated by comma — Type parameters are written inside angle brackets, separated by commas.

Second type parameter

function esle<A, B>(a: A, b: ____): [A, B] { return [a, b]; }

Show answer

function esle<A, B>(a: A, b: B): [A, B] { return [a, b]; }

Multi type parameter parts

<T, U>

Two type parameters
<K, V>

Type parameters for key-value
[U, T]

Reversing type order
cevir<number, string>

Two explicit type arguments

Next lesson: Summary - Generics

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