setter.kt

// This example is lovingly lifted directly from the Kotlin documentation
class Foo() {
    // Note that in Kotlin variable types are inferred, you can say "var" (or val if you want it immutable) instead of specifying the type.
    // Here we are defining a field named "counter" with a value of 1.
    var counter = 0
        // Here we are providing a setter that only updates the field if the new value is positive.
        set(value) {
            if (value >= 0) field = value
        }
}

fun tryItOut() {
    // Hey, here is that val I talked about.
    val foo = Foo()
    
    // You access the field by directly access it (no getCounter())
    val count = foo.counter
    
    // You set the field by directly assigning the value
    // Since we specified a setter is will be implicitly used here
    foo.counter = 2

    // This will not update the value since the conditional in the setter will fail
    foo.counter = -2
}