Intersection-Typen: A und B

Willkommen

Grundlegende Intersection-Syntax

type Named = { name: string };
type Aged = { age: number };
type Person = Named & Aged;
const alice: Person = { name: 'Alice', age: 30 };

Alle Eigenschaften erforderlich

type A = { x: number };
type B = { y: number };
type AB = A & B;
// const p: AB = { x: 1 }; // Error — missing y

Objekttypen zusammenführen

type Serializable = { serialize(): string };
type Loggable = { log(): void };
type Service = Serializable & Loggable;

Intersection im Vergleich zu Extends

// Interface extend:
interface C extends A, B {}

// Intersection type:
type D = A & B;
// Both give the same shape for simple objects

Intersection mit sich widersprechenden Typen

type X = { id: string };
type Y = { id: number };
type XY = X & Y;
// XY.id is string & number = never — impossible!

Intersection in Funktionsparametern

function process(item: Serializable & Loggable): void {
  item.log();
  console.log(item.serialize());
}

Mixin-Muster mit Intersections

type Timestamped<T> = T & { createdAt: Date };
type User = Timestamped<{ name: string; email: string }>;

Intersections primitiver Typen werden zu never

type T = string & number; // never — a value can't be both

Intersection und Union: der zentrale Unterschied

Intersections mit Generics verwenden

type WithId<T> = T & { id: number };
const user: WithId<{ name: string }> = { id: 1, name: 'Alice' };

Kurzer Test

Zusammenfassung