C++ : Examples of virtual functions, without them, and with templates.

main.cpp

#include <iostream>
#include <string>

namespace Without_virtual_functions 
{
	// Without virtual functions
	struct Shape
	{
		std::string description()
		{
			return "shape\n";
		}
	};

	struct Triangle : public Shape
	{
		std::string description()
		{
			return "trinagle\n";
		}
	};

	struct Rectangle : public Shape
	{
		std::string description()
		{
			return "rectangle\n";
		}
	};

	void display(Shape& shape)
	{
		std::cout << shape.description();
	}

	void run()
	{
		Rectangle rec;
		Triangle tri;
		Shape shape;

		display(rec); //I am shape
		display(tri); //I am shape
		display(shape); //I am shape
		std::cout << "-------- \n";
	}
}

namespace With_virtual_functions
{
	// Without virtual functions
	struct Shape
	{
		virtual std::string description()
		{
			return "shape\n";
		}
	};

	struct Triangle : public Shape
	{
		std::string  description() override
		{
			return "trinagle\n";
		}
	};

	struct Rectangle : public Shape
	{
		std::string description() override
		{
			return "rectangle\n";
		}
	};

	void display(Shape& shape)
	{
		std::cout << shape.description();
	}

	void run()
	{
		Rectangle rec;
		Triangle tri;
		Shape shape;

		display(rec); 
		display(tri); 
		display(shape);
		std::cout << "-------- \n";
	}
}

namespace With_templates_example
{
	// Without virtual functions
	struct Shape
	{
		std::string description()
		{
			return "shape\n";
		}
	};

	struct Triangle
	{
		std::string description()
		{
			return "trinagle\n";
		}
	};

	struct Rectangle
	{
		std::string description()
		{
			return "rectangle\n";
		}
	};

	template<typename T>
	void display(T& el)
	{
		std::cout << el.description();
	}

	void run()
	{
		Rectangle rec;
		Triangle tri;
		Shape shape;

		display(rec);
		display(tri);
		display(shape);
		std::cout << "-------- \n";
	}
}


int main()
{
	Without_virtual_functions::run();
	With_virtual_functions::run(); // virtual functions hava a peformace const as there is Vtable but't is not that much
	With_templates_example::run(); // templates generate code at compile time
	return 0;
}