Types and OOP Special type forms

Interfaces, Enums, and Annotations

Beyond regular classes, Klyn provides interfaces for contracts, enums for symbolic states, and annotations for metadata. These three forms are small but important pieces of the language.

Interfaces

interface DoSomething:
    public doSomething() as Int
    public abstract doSomethingElse() as Int

    public static version() as Int:
        return 1

Interface methods are abstract by default. Static interface members are also allowed when they make the contract easier to consume.

Enums

enum Color:
    RED
    GREEN
    BLUE

enum ColorName:
    RED = "red"
    GREEN = "green"
    BLUE = "blue"

    public readonly property value as String

    public ColorName(value as String):
        this.value = value

Simple enums receive integer values by default. You can also define explicit payload values and properties when the enum needs richer data.

Annotations

annotation Deprecated:
    pass

@Deprecated
class LegacyApi:
    pass

Annotations attach metadata to declarations. They are commonly used for testing, tooling, and API lifecycle markers.

Annotations with Arguments

annotation TestClass:
    public readonly property category as String = null

    public TestClass(category as String):
        this.category = category

@TestClass(category="Unit")
class MathTests:
    pass

Annotation arguments use the same named-argument style you see in ordinary calls.

Fully Qualified Annotation Names

@klyn.unittest.TestClass
class DemoTests:
    pass

Qualified annotation names are useful when you want to avoid ambiguity or do not want an extra import for a short file.