Kotlin mutable lazy delegate

MutableLazy.kt

import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

fun <T> mutableLazy(initializer: () -> T) = MutableLazy(initializer)

/**
 * Lazy-like delegate but mutable.
 *
 * Inspired by [SynchronizedLazyImpl] and https://stackoverflow.com/a/47948047/6761823
 */
class MutableLazy<T>(initializer: () -> T, lock: Any? = null) : ReadWriteProperty<Any?, T>, Lazy<T> {
    private object UNINITIALIZED

    private var initializer: (() -> T)? = initializer

    private val lock = lock ?: this

    @Volatile
    private var _value: Any? = UNINITIALIZED

    override var value: T
        get() {
            val v1 = _value
            if (v1 !== UNINITIALIZED) {
                @Suppress("UNCHECKED_CAST")
                return v1 as T
            }

            return synchronized(lock) {
                val v2 = _value
                if (v2 !== UNINITIALIZED) {
                    @Suppress("UNCHECKED_CAST") (v2 as T)
                } else {
                    val typedValue = initializer!!()
                    _value = typedValue
                    initializer = null
                    typedValue
                }
            }
        }
        set(value) = synchronized(lock) {
            _value = value
            initializer = null
        }

    @Suppress("UNCHECKED_CAST")
    override fun getValue(thisRef: Any?, property: KProperty<*>): T = value

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        this.value = value
    }

    override fun isInitialized(): Boolean = _value !== UNINITIALIZED
}