Extensible factory template

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)
project(factory_methods)

set(CMAKE_CXX_STANDARD 17)
add_library(shape_factory shape_factory.cpp)

add_executable(factory_method main.cpp)
target_link_libraries(factory_method shape_factory)

main.cpp

#include "shape_factory.h"
#include <iostream>

class SquareShape : public Shape {
public:
    int GetArea() override {
        return width_ * height_;
    }
    ~SquareShape() override = default;

    static Shape *Create() { return new SquareShape; }
};

int main() {
    //register a new Shape
    ShapeFactory::RegisterShape("square", SquareShape::Create);

    Shape *s = ShapeFactory::CreateShape("square");
    std::cout << "the area of the shape is " << s->GetArea() << std::endl;
    delete s;

    return 0;
}

shape.h

//
// Created by angelos on 06/06/2020.
//

#ifndef FACTORY_METHODS_SHAPE_CLASS_H
#define FACTORY_METHODS_SHAPE_CLASS_H

// interface
class Shape {
public:
    virtual int GetArea() = 0;
    void set_width(int width) { width_ = width; }
    void set_height(int height) { height_ = height; }
    virtual ~Shape() = default;

protected:
    int width_ = 5;
    int height_ = 5;
};

#endif//FACTORY_METHODS_SHAPE_CLASS_H

shape_factory.cpp

//
// Created by angelos on 06/06/2020.
//
#include "shape_factory.h"

CallbackMap ShapeFactory::shapes_;

void ShapeFactory::RegisterShape(std::string_view type, CreateCallback cb) {
    shapes_[type] = cb;
}

void ShapeFactory::UnregisterShape(std::string_view type) {
    shapes_.erase(type);
}

Shape* ShapeFactory::CreateShape(std::string_view type) {
    CallbackMap::iterator it = shapes_.find(type);
    if (it != shapes_.end()) {
        //call the creation callback to constrict the derived type
        return (it->second)();
    }
    return nullptr;
}

shape_factory.h

//
// Created by angelos on 06/06/2020.
//

#ifndef FACTORY_METHODS_SHAPE_FACTORY_H
#define FACTORY_METHODS_SHAPE_FACTORY_H
#include "shape.h"
#include <map>
#include <string_view>

using CreateCallback = Shape* (*)();
using CallbackMap = std::map<std::string_view , CreateCallback>;

class ShapeFactory {
public:
    static void RegisterShape(std::string_view type, CreateCallback cb);
    static void UnregisterShape(std::string_view type);
    static Shape* CreateShape(std::string_view type);

private:
    static CallbackMap shapes_;
};

#endif//FACTORY_METHODS_SHAPE_FACTORY_H