Solution: Observable value
class Observable<T>(initial: T) {
var value: T = initial
set(value) {
field = value
observers.forEach { it(value) }
}
private val observers = mutableListOf<(T) -> Unit>()
fun observe(observer: (T) -> Unit) {
observers.add(observer)
}
}
Example solution in playground
import junit.framework.TestCase.assertTrue
import org.junit.Test
import kotlin.test.assertEquals
class Observable<T>(initial: T) {
var value: T = initial
set(value) {
field = value
observers.forEach { it(value) }
}
private val observers = mutableListOf<(T) -> Unit>()
fun observe(observer: (T) -> Unit) {
observers.add(observer)
}
}
fun main() {
val observable = Observable(1)
println(observable.value) // 1
observable.observe { println("Changed to $it") }
observable.value = 2 // Changed to 2
println(observable.value) // 2
observable.observe { println("now it is $it") }
observable.value = 3
// Changed to 3
// now it is 3
}
class ObservableTest {
@Test
fun `Observable should notify observers`() {
val observable = Observable(1)
var notified = false
observable.observe { notified = true }
observable.value = 2
assertTrue(notified)
}
@Test
fun `Observable should notify all observers`() {
val observable = Observable(1)
var notified1 = false
var notified2 = false
observable.observe { notified1 = true }
observable.observe { notified2 = true }
observable.value = 2
assertTrue(notified1)
assertTrue(notified2)
}
@Test
fun `Observable should notify observers with new value`() {
val observable = Observable(1)
var value = 0
observable.observe { value = it }
observable.value = 2
assertEquals(2, value)
}
}
