FormatDelegate.kt

<!-- Copyright 2019 Google LLC.
SPDX-License-Identifier: Apache-2.0 -->

class FormatDelegate : ReadWriteProperty<Any?, String> {
   private var formattedString: String = ""

   override fun getValue(
       thisRef: Any?,
       property: KProperty<*>
   ): String {
       return formattedString
   }

   override fun setValue(
       thisRef: Any?,
       property: KProperty<*>,
       value: String
   ) {
       formattedString = value.toLowerCase().capitalize()
   }
}

To update FormatDelegate to accept a default value (see comment) this should be:

class FormatDelegate(defaultValue: String = "") : ReadWriteProperty<Any?, String> {
   private var formattedString: String = defaultValue
   ...
}

Any thoughts on defining an interface rather than using Any?

class Person: UpdateCountable {
    override var updateCount: Int = 0
    val firstName: String by CapitalizingUpdateCountableDelegate()
    val lastName: String by CapitalizingUpdateCountableDelegate()
}

interface UpdateCountable {
    var updateCount: Int
}

class CapitalizingUpdateCountableDelegate : ReadWriteProperty<UpdateCountable, String> {
    private var formattedString = ""

    override fun getValue(thisRef: UpdateCountable,
                          property: KProperty<*>): String {
        return formattedString
    }

    override fun setValue(thisRef: UpdateCountable,
                          property: KProperty<*>,
                          value: String) {
        val newValue = value.lowercase().replaceFirstChar { it.uppercase() }

        if (newValue != formattedString) {
            formattedString = newValue
            thisRef.updateCount ++
        }
    }
}