Can you confirm that Delegated Properties are acce...

# reflect

[Daniele B]

Can you confirm that Delegated Properties are accessed only when the variable is read.
For example in this context:

object LocalSettings : SettingsClass() {
    var myString by StringType("mytext")
}


open class SettingsClass {

    val settings = Settings()

    inner class StringType(defaultValue : String) {
        val default = defaultValue
        operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
            return settings.getString(property.name, default)
        }
        operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
            settings.putString(property.name, value)
        }
    }

}

can you confirmed that when the LocalSettings object is instantiated, the StringType delegate will be called only when accessing LocalSettings.myString ?

[diesieben07]

The expression on the right side of by will be evaluated at construction time, i.e. when LocalSettings is instantiated (or in your case, because LocalSettings is an object, when it's class is loaded, which requires JVM details to know exactly when it happens, but basically it's when it's first accessed).
The getValue and setValue will only be called when you get resp. set the myString property.

You can think of by being translated like this:

object LocalSettings : SettingsClass() {
  private val myStringDelegate = StringType("mytext")
  var myString
    get() = myStringDelegate.getValue(this, LocalSettings::myString)
    set(value) {
      myStringDelegate.setValue(this, LocalSettings::myString, value)
    }

[Daniele B]

OK, great, so it looks like it’s behaving the way I meant. Many thanks