add de-sugaring example for chapter 21

src/main/scala/s4j/scala/chapter21/Desugared.scala

@@ -0,0 +1,49 @@
+package s4j.scala.chapter21
+
+object Desugared {
+
+  for (i <- 0 to 5) {
+    println(i)
+  }
+
+  // is de-sugared as
+  (0 to 5).foreach(println)
+
+
+  // nested loop
+  for (i <- 0 to 5; j <- 0 to 5) {
+    println(i + " " + j)
+  }
+
+  // is de-sugared as
+  (0 to 5).foreach { i =>
+    (0 to 5).foreach { j =>
+      println(i + " " + j)
+    }
+  }
+
+
+  // for with yield
+  for (i <- 0 to 5) yield {
+    i + 2
+  }
+
+  // is de-sugared as
+  (0 to 5).map(i => i + 2)
+
+
+  // more interesting example
+  val x: Seq[(Int, Int)] = for {
+    i <- 0 to 5
+    j <- 0 to 5
+  } yield {
+    (i, j)
+  }
+
+  val x2: Seq[(Int, Int)] = (0 to 5).flatMap {
+    i => (0 to 5).map {
+      j => (i, j)
+    }
+  }
+
+}