block14.kt

fun testCoroutine(completion: Continuation<Any?>): Any? {

    class TestContinuation(completion: Continuation<Any?>?) : ContinuationImpl(completion) {
        // Represents the current state of the coroutines state machine
        var label: Int = 0
        // Coroutines results
        var result: Any? = null

        // Used to save the calculation results of the previous coroutine
        var mUser: Any? = null
        var mFriendList: Any? = null

        // invokeSuspend is the key
        // It will eventually call testCoroutine(this)
        // to start the coroutine state machine
        // The state machine code is the when statement below
        // The essence of coroutine is CPS + state machine
        override fun invokeSuspend(_result: Result<Any?>): Any? {
            result = _result
            label = label or Int.Companion.MIN_VALUE
            // testCoroutine(this) could be called several times
            return testCoroutine(this)
        }
    }
}