Generics (জেনেরিক)

// T হলো type parameter — call-এর সময় টাইপ ঠিক হয়
function identity<T>(value: T): T {
  return value;
}

const a = identity("রহিম");   // T = string
const b = identity(42);       // T = number

// বা স্পষ্টভাবে নির্ধারণ
const c = identity<boolean>(true);

function firstElement<T>(arr: T[]): T | undefined {
  return arr[0];
}

const first = firstElement([10, 20, 30]);    // number | undefined
const hello = firstElement(["নমস্কার"]);     // string | undefined

function merge<A, B>(first: A, second: B): A & B {
  return { ...first, ...second };
}

const merged = merge({ name: "রহিম" }, { age: 28 });
// টাইপ: { name: string } & { age: number }

interface HasLength {
  length: number;
}

function longest<A extends HasLength, B extends HasLength>(
  x: A,
  y: B,
): A {
  return x.length >= y.length ? x : y;
}

console.log(longest("বাংলাদেশ", "ভারত"));    // "বাংলাদেশ"

interface ApiResponse<T> {
  data: T;
  status: number;
}

type User = { name: string; id: number };

const response: ApiResponse<User> = {
  status: 200,
  data: { name: "রহিম", id: 1 },
};

// টাইপের ভেতরেও generic
type TList<T> = { items: T[]; count: number };

function createStore<T = string>() {
  return { values: [] as T[] };
}

const store = createStore();          // T = string (default)
const numStore = createStore<number>();  // T = number