Data commit

Task/Gotchas/Wren/gotchas.wren

@@ -0,0 +1,33 @@
+class Rectangle {
+    construct new(width, height) {
+        // Create two fields.
+        _width = width
+        _height = height
+    }
+
+    area {
+       // Here we mis-spell _width.
+       return _widht * _height
+    }
+
+    isSquare {
+        // We inadvertently use '=' rather than '=='.
+        // This sets _width to _height and will always return true
+        // because any number (even 0) is considered 'truthy' in Wren.
+        if (_width = _height) return true
+        return false
+    }
+
+    diagonal {
+        // We use 'sqrt' instead of the Math.sqrt method.
+        // The compiler thinks this is an instance method of Rectangle
+        // which will be defined later.
+        return sqrt(_width * _width + _height * _height)
+    }
+}
+
+var rect = Rectangle.new(80, 100)
+System.print(rect.isSquare) // returns true which it isn't!
+System.print(rect.area)     // runtime error: Null does not implement *(_)
+System.print(rect.diagonal) // runtime error (if previous line commented out)
+                            // Rectangle does not implement 'sqrt(_)'