Channel operators (#88)

integration/kotlinx-coroutines-jdk8/src/main/kotlin/kotlinx/coroutines/experimental/channels8/Channels.kt

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+/*
+ * Copyright 2016-2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kotlinx.coroutines.experimental.channels8
+
+import kotlinx.coroutines.experimental.CommonPool
+import kotlinx.coroutines.experimental.channels.ProducerJob
+import kotlinx.coroutines.experimental.channels.ReceiveChannel
+import kotlinx.coroutines.experimental.channels.consumeEach
+import kotlinx.coroutines.experimental.channels.produce
+import kotlinx.coroutines.experimental.runBlocking
+import java.util.*
+import java.util.function.BiConsumer
+import java.util.function.Consumer
+import java.util.stream.Collector
+import java.util.stream.Stream
+import java.util.stream.StreamSupport
+import kotlin.coroutines.experimental.CoroutineContext
+
+/**
+ * Creates a [ProducerJob] to read all element of the [Stream].
+ */
+public fun <E> Stream<E>.asReceiveChannel(context: CoroutineContext = CommonPool): ProducerJob<E> = produce(context) {
+    for (element in this@asReceiveChannel)
+        send(element)
+}
+
+/**
+ * Creates a [Stream] of elements in this [ReceiveChannel].
+ */
+public fun <E : Any> ReceiveChannel<E>.asStream(): Stream<E> = StreamSupport.stream<E>(SpliteratorAdapter(this), false)
+
+/**
+ * Applies the [collector] to the [ReceiveChannel]
+ */
+public suspend fun <T, A : Any, R> ReceiveChannel<T>.collect(collector: Collector<T, A, R>): R {
+    val container: A = collector.supplier().get()
+    val accumulator: BiConsumer<A, T> = collector.accumulator()
+    consumeEach { accumulator.accept(container, it) }
+    return collector.finisher().apply(container)
+}
+
+private class SpliteratorAdapter<E : Any>(val channel: ReceiveChannel<E>) : Spliterator<E> {
+    override fun estimateSize(): Long = Long.MAX_VALUE
+
+    override fun forEachRemaining(action: Consumer<in E>) {
+        runBlocking {
+            for (element in channel)
+                action.accept(element)
+        }
+    }
+
+    override fun tryAdvance(action: Consumer<in E>): Boolean = runBlocking {
+        val element = channel.receiveOrNull()
+        if (element != null) {
+            action.accept(element)
+            true
+        } else false
+    }
+
+    override fun characteristics(): Int = characteristics
+
+    override fun trySplit(): Spliterator<E>? = null
+
+    private companion object {
+        @JvmStatic
+        private val characteristics = Spliterator.ORDERED or Spliterator.NONNULL
+    }
+}

integration/kotlinx-coroutines-jdk8/src/test/kotlin/kotlinx/coroutines/experimental/channels8/ChannelsTest.kt

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+package kotlinx.coroutines.experimental.channels8
+
+import kotlinx.coroutines.experimental.TestBase
+import kotlinx.coroutines.experimental.channels.asReceiveChannel
+import kotlinx.coroutines.experimental.channels.toList
+import kotlinx.coroutines.experimental.runBlocking
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import java.util.stream.Collectors
+
+class ChannelsTest : TestBase() {
+    private val testList = listOf(1, 2, 3)
+
+    @Test
+    fun testCollect() = runBlocking {
+        assertEquals(testList, testList.asReceiveChannel().collect(Collectors.toList()))
+    }
+
+    @Test
+    fun testStreamAsReceiveChannel() = runBlocking {
+        assertEquals(testList, testList.stream().asReceiveChannel().toList())
+    }
+
+    @Test
+    fun testReceiveChannelAsStream() {
+        assertEquals(testList, testList.asReceiveChannel().asStream().collect(Collectors.toList()))
+    }
+}