make ReadStateChannel into a monad

tindzk · Apr 26, 2016 · faadfbe · faadfbe
1 parent 6635617
commit faadfbe
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Showing 2 changed files with 20 additions and 1 deletion.
diff --git a/shared/src/main/scala/pl/metastack/metarx/Channel.scala b/shared/src/main/scala/pl/metastack/metarx/Channel.scala
@@ -736,6 +736,14 @@ trait RootChannel[T]
 
 trait ReadStateChannel[T] extends ReadChannel[T] {
   def get: T
+
+  def flatMap[U](f: T => ReadStateChannel[U]): ReadStateChannel[U] = {
+    flatMap(f.asInstanceOf[T => ReadChannel[U]]).cache(f(get).get)
+  }
+
+  override def map[U](f: T => U): ReadStateChannel[U] = {
+    flatMap { x => Var(f(x)) }
+  }
 }
 
 /** In Rx terms, a [[StateChannel]] can be considered a cold observable. */

diff --git a/shared/src/test/scala/pl/metastack/metarx/ChannelTest.scala b/shared/src/test/scala/pl/metastack/metarx/ChannelTest.scala
@@ -480,12 +480,23 @@ class ChannelTest extends CompatTest {
   test("flatMap() (3)") {
     var value = ""
     Var(42)
-      .flatMap(x => Var(x.toString))
+      .flatMap((x: Int) => Var(x.toString))
       .filter(_ => true)
       .attach(value = _)
     assertEquals(value, "42")
   }
 
+  test("flatMap() (4)") {
+    val v1 = Var(42)
+    val v2 = v1.map((x: Int) => x + 1)
+    var resultList: List[Int] = List.empty
+    v2.attach{ x => resultList = resultList ++ List(x) }
+    assertEquals (v2.get, 43)
+    v1.update(_ => 43)
+    assertEquals(v2.get, 44)
+    assertEquals(resultList, List(43, 44))
+  }
+
   test("flatMapCh()") {
     val ch = Channel[Var[Int]]()
     val a = ch.flatMapCh(cur => cur)