done shape marker example form tutorial point

Author: AdelDaniel

structural_design_pattern/facade/shape_maker.dart

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+//!
+//! BAD EXAMPLE FROM TUTORIAL POINT
+//! Source:: https://www.tutorialspoint.com/design_pattern/facade_pattern.htm
+
+// ShapeMaker class uses the concrete classes to delegate user calls to these classes.
+// main, our demo class, will use ShapeMaker class to show the results.
+
+// Step 1
+// Create an interface.
+abstract class IShape {
+  void draw();
+}
+
+// Step 2
+// Create concrete classes implementing the same interface.
+class Rectangle implements IShape {
+  @override
+  void draw() => print("Rectangle::draw()");
+}
+
+class Square implements IShape {
+  @override
+  void draw() => print("Square::draw()");
+}
+
+class Circle implements IShape {
+  @override
+  void draw() => print("Circle::draw()");
+}
+
+// Step 3
+// Create a facade class.
+class ShapeMaker {
+  IShape _circle;
+  IShape _rectangle;
+  IShape _square;
+
+  ShapeMaker()
+      : _circle = Circle(),
+        _rectangle = Rectangle(),
+        _square = Square();
+
+  void drawCircle() => _circle.draw();
+  void drawRectangle() => _rectangle.draw();
+  void drawSquare() => _square.draw();
+}
+
+// Step 4
+// Use the facade to draw various types of shapes.
+void main() {
+  ShapeMaker shapeMaker = ShapeMaker();
+
+  shapeMaker.drawCircle();
+  shapeMaker.drawRectangle();
+  shapeMaker.drawSquare();
+}
+
+// Step 5
+// output.
+// Circle::draw()
+// Rectangle::draw()
+// Square::draw()