Custom class for delegation

When to use custom delegate class?

Centralize the implementation of a property and make it more reusable and easier to maintain.
This way, you can reduce duplicated code

Imagine you should logging property read count.
If you define custom get() and set() per every property, there should occur duplicates code.

Example code

class ReadCountTest {
    class AutoIncrementCount {
        private var count: Int = 0
        operator fun getValue(thisRef: Any?, property: KProperty<*>): Int {
            ++count
            return count
        }
        // not defined 'setValue()' method
        // so this is for value property.
    }

    class Board() {
        val readCount: Int by AutoIncrementCount()
    }

    @DisplayName("property read count")
    @Test
    internal fun testCount() {
        val board = Board()
        assertEquals(1, board.readCount)
        assertEquals(2, board.readCount)
        assertEquals(3, board.readCount)
    }
}