Simple factory pattern example

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>

int main() {

    auto my_shape = ShapeFactory::CreateShape(Shapes::kTriangle);

    std::cout << "the are of the shape is " << my_shape->GetArea() << std::endl;
    return 0;
}

rectangle.h

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

#ifndef FACTORY_METHODS_RECTANGLE_H
#define FACTORY_METHODS_RECTANGLE_H
#include "shape.h"

class Rectangle : public Shape {
public:
    int GetArea() override {
        return (width_*height_);
    }
};
#endif//FACTORY_METHODS_RECTANGLE_H

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; }

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"
#include "rectangle.h"
#include "triangle.h"

Shape* ShapeFactory::CreateShape(Shapes type) {
    if (type == Shapes::kRectangle) {
        return new Rectangle;
    }
    if (type == Shapes::kTriangle) {
        return new Triangle;
    }
}

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"

enum class Shapes { kRectangle,
                    kTriangle };

class ShapeFactory {
public:
    static Shape *CreateShape(Shapes type);
};

#endif//FACTORY_METHODS_SHAPE_FACTORY_H

triangle.h

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

#ifndef FACTORY_METHODS_TRIANGLE_H
#define FACTORY_METHODS_TRIANGLE_H
#include "shape.h"

class Triangle : public Shape {
public:
    int GetArea() override {
        return (width_*height_)/2;
    }
};

#endif//FACTORY_METHODS_TRIANGLE_H