Best method to implement an abstract factory pattern

Question

Consider following code:

#include 


// =============================


class Shape{
public:
    virtual ~Shape(){};

    virtual void process         


        

Answer 1

Your factories are passing around ownership. There's another alternative to that aspect; instead of passing around ownership, you can make the factory own the objects:

   class Factory {
   public:
      ~Factory() { for(int i=0;i<vec.size();i++) delete vec[i]; }
      Shape &build_obj() {
         Shape *sh = new Triangle;
         vec.push_back(sh);
         return *sh;
       }

   private:
      void operator=(const Factory &);
      std::vector<Shape*> vec;
   };

Answer 2

I think the most idiomatic modern C++ method is the one you mention in passing but ignore. Return a std::unique_ptr<Shape>.

It is safe, clearly expresses ownership, supports polymorphism and doesn't need much code.

class ShapeFactory {
public:
  std::unique_ptr<Shape> create(){
    return std::make_unique<Triangle>();
  }
};

But I wouldn't want to claim it was the "best" method.

Your PimplShape in option 3 is actually very similar to a unique_ptr just less generic or tested.