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Master Software Design Patterns and Architecture in C++

Solution: Factory Method

Explore the factory method design pattern by learning to create cloneable objects in C++ using std::shared_ptr. Understand how to refactor code for flexible window objects and create a perfect factory method that returns clones of various types. This lesson helps you grasp object-oriented design principles critical for scalable software development.

We'll cover the following...

Solution to the first problem

Here is the refactored code using std::shared_ptr.

C++
#include <iostream>
#include <memory>
// Product
class Window{ 
  public: 
    virtual std::shared_ptr<Window> clone() = 0; 
};
// Concrete Products 
class DefaultWindow: public Window {
  public:
    DefaultWindow() {
      std::cout << "DefaultWindow" << '\n';
    }
  private:
    std::shared_ptr<Window> clone() override { 
      return std::make_shared<DefaultWindow>();
    } 
};
class FancyWindow: public Window {
  public:
    FancyWindow() {
      std::cout << "FancyWindow" << '\n';
    }
  private:
    std::shared_ptr<Window> clone() override { 
      return std::make_shared<FancyWindow>();
    } 
};
// Concrete Creator or Client
auto getNewWindow(std::shared_ptr<Window> oldWindow) { 
  return oldWindow->clone();
}
  
int main() {
  std::shared_ptr<Window> defaultWindow = std::make_shared<DefaultWindow>();
  std::shared_ptr<Window> fancyWindow = std::make_shared<FancyWindow>();
  
  auto defaultWindow1 = getNewWindow(defaultWindow);
  auto fancyWindow1 = getNewWindow(fancyWindow);
  
}

Code explanation

  • Lines 4–8: We created a Window base class with one pure virtual method clone() with a std::shared_ptr return type.

  • Lines 11–20: We created a DefaultWindow class derived from the Window parent class. We created a constructor with no parameters, ...