Generics in TypeScript

// Generic function
function identity<T>(value: T): T {
    return value;
}
identity<string>('hello'); // returns string
identity<number>(42);      // returns number

// Generic interface
interface ApiResponse<T> {
    data: T;
    status: number;
    message: string;
}

interface User { id: number; name: string; }

const response: ApiResponse<User[]> = {
    data: [{ id: 1, name: 'Alice' }],
    status: 200,
    message: 'OK',
};

// Generic class
class Stack<T> {
    private items: T[] = [];

    push(item: T): void { this.items.push(item); }
    pop(): T | undefined { return this.items.pop(); }
    peek(): T | undefined { return this.items[this.items.length - 1]; }
    get size(): number { return this.items.length; }
}

const numStack = new Stack<number>();
numStack.push(1);
numStack.push(2);
console.log(numStack.pop()); // 2

// Constrained generic
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
    return obj[key];
}