lecture 3 stuff

lectures/03/square.rs

@@ -0,0 +1,15 @@
+// simple example of extension trait
+// how to add square method to i32
+trait Square {
+    fn square(self) -> Self;
+}
+
+impl Square for i32 {
+    fn square(self) -> Self {
+        self * self
+    }
+}
+
+fn main() {
+    println!("{}", 32.square());
+}