Mastering High Performance with Kotlin

Creating a delegated property

For a read-only property marked with the val keyword, a delegated class has to have a getValue() method that takes the following arguments:

• thisRef: A reference to a delegating object
• property: An instance of the KProperty class

An instance of the KProperty type can be used to retrieve metadata about a property.

The getValue() method also has to return an instance that has the same type or supertype as a delegating property. It can be an extension function, as in the case of the Lazy class.

For a property marked with the var keyword, a delegate class also has to have a setValue() method that takes the following arguments:

• thisRef: A reference to an outer class
• property: An instance of the KProperty type