G17_Visitor.cpp

/**************************************************************************************************
*
* \file G17_Visitor.cpp
* \brief Guideline 17: Consider std::variant for Implementing Visitors
*
* Copyright (C) 2022 Klaus Iglberger - All Rights Reserved
*
* This file is part of the supplemental material for the O'Reilly book "C++ Software Design"
* (https://www.oreilly.com/library/view/c-software-design/9781098113155/).
*
**************************************************************************************************/


//---- <Point.h> ----------------------------------------------------------------------------------

struct Point
{
   double x;
   double y;
};


//---- <Circle.h> ---------------------------------------------------------------------------------

//#include <Point.h>

class Circle
{
 public:
   explicit Circle( double radius )
      : radius_( radius )
   {
      /* Checking that the given radius is valid */
   }

   double radius() const { return radius_; }
   Point  center() const { return center_; }

 private:
   double radius_;
   Point center_{};
};


//---- <Square.h> ---------------------------------------------------------------------------------

//#include <Point.h>

class Square
{
 public:
   explicit Square( double side )
      : side_( side )
   {
      /* Checking that the given side length is valid */
   }

   double side  () const { return side_; }
   Point  center() const { return center_; }

 private:
   double side_;
   Point center_{};
};


//---- <Shape.h> ----------------------------------------------------------------------------------

//#include <Circle.h>
//#include <Square.h>
#include <variant>

using Shape = std::variant<Circle,Square>;


//---- <Shapes.h> ----------------

//#include <Shape.h>
#include <vector>

using Shapes = std::vector<Shape>;


//---- <Draw.h> -----------------------------------------------------------------------------------

//#include <Circle.h>
//#include <Square.h>
//#include /* some graphics library */

class Draw
{
 public:
   void operator()( Circle const& c ) const
   {
      /* ... Implementing the logic for drawing a circle ... */
   }
   void operator()( Square const& s ) const
   {
      /* ... Implementing the logic for drawing a square ... */
   }
};


//---- <DrawAllShapes.h> --------------------------------------------------------------------------

//#include <Shapes.h>

void drawAllShapes( Shapes const& shapes );


//---- <DrawAllShapes.cpp> ------------------------------------------------------------------------

//#include <DrawAllShapes.h>
//#include <Draw.h>

void drawAllShapes( Shapes const& shapes )
{
   for( auto const& shape : shapes )
   {
      std::visit( Draw{}, shape );
   }
}


//---- <Main.cpp> ---------------------------------------------------------------------------------

//#include <Circle.h>
//#include <Square.h>
//#include <Shapes.h>
//#include <DrawAllShapes.h>
#include <cstdlib>

int main()
{
   Shapes shapes;

   shapes.emplace_back( Circle{ 2.3 } );
   shapes.emplace_back( Square{ 1.2 } );
   shapes.emplace_back( Circle{ 4.1 } );

   drawAllShapes( shapes );

   return EXIT_SUCCESS;
}