Scala : sandbox: Scala : add 7-variance

2 files changed, 26 insertions, 0 deletions

diff --git a/Scala/sandbox/0-main.scala b/Scala/sandbox/0-main.scala
index 99ee4ba..6f0edf3 100644
--- a/Scala/sandbox/0-main.scala
+++ b/Scala/sandbox/0-main.scala
@@ -9,5 +9,6 @@ object Main  extends App {
     IntSet.run
     IntList.run
     Natural.run
+    Variance.run
 
 }
diff --git a/Scala/sandbox/7-variance.scala b/Scala/sandbox/7-variance.scala
new file mode 100644
index 0000000..49f0373
--- /dev/null
+++ b/Scala/sandbox/7-variance.scala
@@ -0,0 +1,25 @@
+object Variance
+{
+  // to allow 
+  trait List[+T] {
+    def isEmpty: Boolean
+    def head: T
+    def tail: List[T]
+  }
+
+  class Cons[T](val head: T, val tail: List[T]) extends List[T] {
+    def isEmpty = false
+  }
+
+  // extends List[Nothing] so that it can hold anything
+  object Nil extends List[Nothing] {
+    def isEmpty = true
+    def head: Nothing = throw new NoSuchElementException("Nil.head")
+    def tail: Nothing = throw new NoSuchElementException("Nil.tail")
+  }
+
+  def run = {
+    println("Variance")
+    val x: List[String] = Nil
+  }
+}