Alias de types pour les types complexes

type UserId = number;
type UserName = string;
type Point = { x: number; y: number };

type StringOrNumber = string | number;
function format(val: StringOrNumber): string {
  return String(val);
}

type Product = {
  id: number;
  name: string;
  price: number;
};
const p: Product = { id: 1, name: 'Widget', price: 9.99 };

type Coordinate = [number, number];
type RGB = [number, number, number];
const pos: Coordinate = [10, 20];

type Comparator<T> = (a: T, b: T) => number;
const numSort: Comparator<number> = (a, b) => a - b;

type Maybe<T> = T | null | undefined;
type Pair<A, B> = { first: A; second: B };

type TreeNode = {
  value: number;
  left?: TreeNode;
  right?: TreeNode;
};

// Interface can be merged (declaration merging):
interface A { x: number; }
interface A { y: number; } // OK — A now has x and y

// Type alias cannot:
type B = { x: number };
// type B = { y: number }; // Error: duplicate identifier

type Success = { kind: 'success'; data: string };
type Failure = { kind: 'failure'; error: Error };
type Result = Success | Failure;