C++ : Implicit conversion example, explicit keyword

main.cpp

#include <iostream>

namespace Without_explicit
{
	struct Entity
	{
		int a;
		int b;

		Entity(int a, int b) : a{ a }, b{ b }
		{
		}

		Entity(int a) : a{ a }, b{ -1 }
		{

		}

		void print()
		{
			std::cout << "a : " << a << " b : " << b << " \n";
		}
	};

	void run()
	{
		{
			Entity e = 5; //implicit conversin takes place
			e.print(); //5, -1
		}

		{
			Entity e(10, 20);
			e.print(); //10, 20
		}

		{
			Entity e = (Entity)5; //explicid conversion
			e.print(); //5 - 1
		}
	}
}


namespace With_explicit
{
	struct Entity
	{
		int a;
		int b;

		explicit Entity(int a, int b) : a{ a }, b{ b }
		{
		}

		explicit Entity(int a) : a{ a }, b{ -1 }
		{

		}

		void print()
		{
			std::cout << "a : " << a << " b : " << b << " \n";
		}
	};

	void run()
	{
		//This case will not run as implicid conversion is not allowed
		{
			//Entity e = 5; //implicit conversin takes place
			//e.print(); //5, -1
		}

		{
			Entity e(10, 20);
			e.print(); //10, 20
		}

		{
			Entity e = (Entity)5; //explicid conversion
			e.print(); //5 - 1
		}
	}
}

int main()
{
	Without_explicit::run();
	std::cout << "-----------\n";
	With_explicit::run();
}