Generics

1// Generic function
2function identity<T>(value: T): T {
3  return value;
4}
5 
6const num = identity(42);        // type: number
7const str = identity("hello");   // type: string
8 
9// Generic with constraints
10interface HasLength {
11  length: number;
12}
13 
14function logLength<T extends HasLength>(value: T): T {
15  console.log(`Length: ${value.length}`);
16  return value;
17}
18 
19logLength("hello");      // Length: 5
20logLength([1, 2, 3]);    // Length: 3
21// logLength(42);        // Error: number doesn't have length
22 
23// Generic interface
24interface Result<T> {
25  data: T;
26  success: boolean;
27  timestamp: Date;
28}
29 
30const userResult: Result<{ name: string }> = {
31  data: { name: "Alice" },
32  success: true,
33  timestamp: new Date(),
34};
35 
36// Generic class
37class Stack<T> {
38  private items: T[] = [];
39 
40  push(item: T): void {
41    this.items.push(item);
42  }
43 
44  pop(): T | undefined {
45    return this.items.pop();
46  }
47 
48  peek(): T | undefined {
49    return this.items[this.items.length - 1];
50  }
51}
52 
53const numberStack = new Stack<number>();
54numberStack.push(1);
55numberStack.push(2);
56console.log(numberStack.pop()); // 2
57 
58// Multiple type parameters
59function pair<K, V>(key: K, value: V): [K, V] {
60  return [key, value];
61}
62 
63const kvPair = pair("name", "Alice"); // [string, string]
64const mixedPair = pair(1, true);      // [number, boolean]