Understanding universal references

As we discussed in the previous article, && means universal references when type deduction is involved.
But internally, the template parameter is getting instantiated twice, once of Lvalue and the other Rvalue. The below program demonstrates it.

	#include <iostream>
	template<typename T>
	void func(T&& param)
	{
	static int x = 0;
	std::cout << "Value is " << x << '\n';
	++x;
	}
	int main()
	{
	int x = 2;
	func(x);
	func(2);
	func(x);
	func(2);
	}
	/* Output
	Value is 0
	Value is 0
	Value is 1
	Value is 1
	*/

view raw universal_references.cpp hosted with ❤ by GitHub

In this code, when func is called with x, the int Lvalue version of it gets instantiated.  i.e

	void func(int& param)
	{
	static int x = 0;
	std::cout << "Value is " << x << '\n';
	++x;
	}

view raw Lvalue_version.cpp hosted with ❤ by GitHub

When func is called the second time with 2, the int Rvalue version of it gets instantiated (see code below). Hence the value count is 0 in both the cases.

	void func(int&& param)
	{
	static int x = 0;
	std::cout << "Value is " << x << '\n';
	++x;
	}

view raw Rvalue_version.cpp hosted with ❤ by GitHub