What types of delegates exist in Kotlin?

Property Delegates: Allow reusing common logic for getting/setting property values. Examples:

• lazy: Lazy initialization of a property.
• observable: Notifies about changes in the property value.
• vetoable: Allows canceling a change in the property value.
• Properties stored in a Map.

// Lazy initialization
val lazyValue: String by lazy {
    println("Calculating lazyValue...")
    "Hello"
}

// Observable property
var name: String by Delegates.observable("initial value") {
    prop, old, new ->
    println("$old -> $new")
}

Delegating Implementation of Interfaces: Allows passing the implementation of an interface to another object. This is the "decorator" pattern.

interface Base {
    fun print()
}

class BaseImpl(val x: Int) : Base {
    override fun print() {
        print(x)
    }
}

class Derived(b: Base) : Base by b // Delegating the implementation of Base