Kotlin: Different property delegates for same property

Vairavan Srinivasan

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Nov 18, 2023

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Kotlin’s property delegation is straight forward for most cases. However, there are scenarios where one would like to change the actual delegate based on other runtime conditions.

In the following case, a PropertyDelegateProvider is used to provide different delegates for debug and release versions by overriding operator function provideDelegate.

open class PropertyDelegate<out T>(private val value: T): ReadOnlyProperty<Any?, T> {
    override operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return value
    }
}

class DebugPropertyDelegate<out T>(private val value: T): PropertyDelegate<T>(value) {
    override operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
        // Log in debug version
        return value
    }
}

class PropertyDelegateProvider<out T>(private val value: T) {
    operator fun provideDelegate(
        thisRef: Any?,
        property: KProperty<*>
    ): PropertyDelegate<T> {
        return when {
            isDebug -> DebugPropertyDelegate(value)
            else -> PropertyDelegate(value)
        }
    }
}

The delegate provider can then be used at call site without any runtime checks.

val value by PropertyDelegateProvider(10)