What are type aliases and when should you use them?

Type aliases create alternative names for existing types, improving code readability and maintainability.\n\n**Basic type aliases:**\n\ntypealias UserId = Int\ntypealias UserName = String\ntypealias EmailAddress = String\n\nfun createUser(id: UserId, name: UserName, email: EmailAddress) {\n // Implementation\n}\n\n// Usage\nval userId: UserId = 123\nval userName: UserName = "John Doe"\nval email: EmailAddress = "john@example.com"\n\n\n**Function type aliases:**\n\ntypealias EventHandler = (String) -> Unit\ntypealias Predicate = (T) -> Boolean\ntypealias Transformer = (T) -> R\n\nclass EventManager {\n private val handlers = mutableListOf()\n \n fun addHandler(handler: EventHandler) {\n handlers.add(handler)\n }\n \n fun fireEvent(event: String) {\n handlers.forEach { it(event) }\n }\n}\n\n// Usage\nval logger: EventHandler = { event -> println("Log: $event") }\nval emailer: EventHandler = { event -> sendEmail(event) }\n\n\n**Generic type aliases:**\n\ntypealias StringMap = Map\ntypealias MutableStringMap = MutableMap\ntypealias NodeList = List>\n\n// Usage\nval userPreferences: StringMap = mapOf(\n "theme" to "dark",\n "language" to "en"\n)\n\nval cache: MutableStringMap = mutableMapOf()\n\n\n**Complex type aliases:**\n\ntypealias ApiResponse = Result\ntypealias ValidationResult = Either, ValidatedData>\ntypealias DatabaseConnection = Connection\n\n// Nested generics\ntypealias UserRepository = Repository\ntypealias AsyncResult = CompletableFuture>\n\n\n**Class and interface aliases:**\n\ntypealias MyList = ArrayList\ntypealias StringProcessor = Function\n\nclass DataProcessor {\n private val items: MyList = MyList()\n private val processor: StringProcessor = { it.uppercase() }\n}\n\n\n**When to use type aliases:**\n\n**✅ Good use cases:**\n• Simplifying complex generic types\n• Creating domain-specific names for primitive types\n• Shortening frequently used function types\n• Improving API readability\n• Reducing repetition in type declarations\n\n**❌ Avoid when:**\n• You need type safety (use value classes instead)\n• The alias doesn't add clarity\n• It's used only once or twice\n• It makes code less clear\n\n**Type aliases vs Value classes:**\n\n// Type alias - no runtime type safety\ntypealias UserId = Int\nfun getUser(id: UserId): User = TODO()\nfun getOrder(id: Int): Order = TODO()\n\nval userId: UserId = 123\ngetOrder(userId) // Compiles but wrong!\n\n// Value class - runtime type safety\n@JvmInline\nvalue class UserId(val value: Int)\n\nval userId = UserId(123)\n// getOrder(userId) // Compilation error!\n\n\n**Nested type aliases:**\n\nclass OuterClass {\n typealias InnerAlias = String\n \n fun process(value: InnerAlias) {\n println(value)\n }\n}\n\n// Access nested alias\ntypealias GlobalInnerAlias = OuterClass.InnerAlias\n\n\n**Import aliases:**\n\nimport com.example.ui.Button as UiButton\nimport com.example.data.Button as DataButton\n\n// Now can use both without conflict\nval uiButton = UiButton()\nval dataButton = DataButton()\n