Attributes and Properties

public class Rational:
    private _numerator as Int
    private _denominator as Int

Backing fields usually carry a leading underscore and stay private to the class.

public property denominator as Int:
    get:
        return this._denominator
    set:
        if value == 0:
            throw ValueException("denominator cannot be 0")
        this._denominator = value

Properties can enforce validation or compute values before they expose data.

public class Point:
    public property x = 0
    public property y = 0

Auto-properties are ideal when you want a normal property surface but do not need custom getter or setter logic.

import klyn.collections

class Project:
    public readonly property name as String
    public readonly property files as ArrayList<String>

    public Project(name as String):
        this.name = name
        this.files = []

project = Project("Klyn")
# project.name = "renamed"      # Compile-time error: no writable setter.
project.files.add("main.kn")    # Allowed: readonly is shallow.

Use readonly when callers may observe a property but must not replace its value. This is a shallow restriction: if the property returns a mutable object, that object's own API remains usable. Unlike a class-level const, a readonly property is not an implicitly static constant; its getter may return instance state or compute a value on every access. Use an immutable collection or value type when deep immutability is required.

Add signal when a property represents observable state. Assignment keeps the same property syntax, but the compiler compares the old and new values and notifies the shared binding engine automatically when the value actually changes. Application code must not call Binding.notify() itself.

import klyn.binding

public class Counter:
    public signal property value as Int = 0

counter = Counter()
mirror = Counter()
Binding.oneWay(counter::value, mirror::value)

counter.value = 1
assert mirror.value == 1

Use signal properties for durable state such as text, selection, progress, or a current value. Use an event instead for a one-shot action such as a click. The complete distinction is covered in Signals vs Events.

r = Rational(1, 3)
print(r.numerator)
r.denominator = 5

Properties use ordinary member access syntax. Callers do not need to know whether the property is auto-implemented or backed by custom getter and setter blocks.