startUndispatchedCoroutine utility functions

Author: elizarov

kotlinx-coroutines-core/src/main/kotlin/kotlinx/coroutines/experimental/intrinsics/Undispatched.kt

@@ -0,0 +1,39 @@
+package kotlinx.coroutines.experimental.intrinsics
+
+import kotlin.coroutines.experimental.Continuation
+import kotlin.coroutines.experimental.intrinsics.COROUTINE_SUSPENDED
+import kotlin.coroutines.experimental.suspendCoroutine
+
+/**
+ * Use this function to restart coroutine directly from inside of [suspendCoroutine].
+ *
+ * @suppress **This is unstable API and it is subject to change.**
+ */
+@Suppress("PLATFORM_CLASS_MAPPED_TO_KOTLIN", "UNCHECKED_CAST")
+internal fun <R> (suspend () -> R).startUndispatchedCoroutine(completion: Continuation<R>) {
+    val value = try {
+        (this as kotlin.jvm.functions.Function1<Continuation<R>, Any?>).invoke(completion)
+    } catch (e: Throwable) {
+        completion.resumeWithException(e)
+        return
+    }
+    if (value !== COROUTINE_SUSPENDED)
+        completion.resume(value as R)
+}
+
+/**
+ * Use this function to restart coroutine directly from inside of [suspendCoroutine].
+ *
+ * @suppress **This is unstable API and it is subject to change.**
+ */
+@Suppress("PLATFORM_CLASS_MAPPED_TO_KOTLIN", "UNCHECKED_CAST")
+internal fun <E, R> (suspend (E) -> R).startUndispatchedCoroutine(element: E, completion: Continuation<R>) {
+    val value = try {
+        (this as kotlin.jvm.functions.Function2<E, Continuation<R>, Any?>).invoke(element, completion)
+    } catch (e: Throwable) {
+        completion.resumeWithException(e)
+        return
+    }
+    if (value !== COROUTINE_SUSPENDED)
+        completion.resume(value as R)
+}