// TypeScript Generics - Advanced Patterns // Note: This is a read-only preview // 1. Basic Generic Function function identity(arg: T): T { return arg; } const num = identity(42); // type: number const str = identity("hello"); // type: string // 2. Generic Constraints interface HasLength { length: number; } function logLength(arg: T): T { console.log(`Length: ${arg.length}`); return arg; } logLength("hello"); // OK - string has length logLength([1, 2, 3]); // OK - array has length // logLength(42); // Error - number has no length // 3. Generic Interface interface ApiResponse { data: T; status: number; message: string; } interface User { id: number; name: string; email: string; } type UserResponse = ApiResponse; type UsersResponse = ApiResponse; // 4. Generic Class class Stack { 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 numberStack = new Stack(); numberStack.push(1); numberStack.push(2); // 5. Mapped Types type ReadonlyType = { readonly [P in keyof T]: T[P] }; type PartialType = { [P in keyof T]?: T[P] }; type RequiredType = { [P in keyof T]-?: T[P] }; // 6. Conditional Types type IsString = T extends string ? "yes" : "no"; type A = IsString; // "yes" type B = IsString; // "no" // 7. Generic Utility Function function groupBy(array: T[], key: K): Record { return array.reduce((result, item) => { const group = String(item[key]); (result[group] = result[group] || []).push(item); return result; }, {} as Record); } const users = [ { name: "Alice", role: "admin" }, { name: "Bob", role: "user" }, { name: "Charlie", role: "admin" }, ]; const grouped = groupBy(users, "role"); // { admin: [Alice, Charlie], user: [Bob] }