Challenge 3: A Custom Range-Clamping Delegate — Solution

import kotlin.reflect.KProperty

class RangeClamped(private var value: Int, private val range: IntRange) {
    operator fun getValue(thisRef: Any?, property: KProperty<*>): Int {
        return value
    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, newValue: Int) {
        value = newValue.coerceIn(range)
    }
}

class Display {
    var brightness: Int by RangeClamped(50, 0..100)
}

fun main() {
    val display = Display()
    println(display.brightness)

    display.brightness = 150
    println(display.brightness)

    display.brightness = -20
    println(display.brightness)
}

/*
Output:
50
100
0

Notes:
- setValue uses the standard library's coerceIn(range) to clamp any
  assigned value into the allowed range before storing it — assigning
  150 to a 0..100 range stores 100, and assigning -20 stores 0.
- getValue simply returns the already-clamped stored value, so reads
  never need to reapply the clamp.
- Because RangeClamped implements getValue/setValue as operator
  functions, it works with the "by" keyword exactly like the built-in
  delegates (lazy, observable) covered earlier in the chapter.
*/