Suspended Variable

suspend_var_actorless.kt

/**
 * kinda like `lateinit var` but if it's really late it will make you wait rather than crash.
 */
class SuspendedVariable<T> {
    private val callbacks = mutableListOf<((T) -> Unit)>()
    private var value: T? = null

    fun set(t: T) {
        value = t
        if (t != null) {
            callbacks.forEach { it(t) }
            callbacks.clear()
        }
    }

    suspend fun get() : T = suspendCancellableCoroutine { continuation ->
        value?.let {
            continuation.resume(it)
            return@suspendCancellableCoroutine
        }

        val callback = { value : T ->
            continuation.resume(value)
        }

        callbacks += callback

        continuation.invokeOnCancellation {
            callbacks -= callback
        }
    }
}