reference_wrapper in C++

std::reference_wrapper is a class template that wraps a reference in a copy constructible and copy assignable object or reference to function of type T.
Instances of std::reference_wrapper are objects (they can be copied or stored in containers) but they are implicitly convertible to ‘T&’ so that they can be used as arguments with the functions that take the underlying type by reference.

Syntax:

template <class T> class reference_wrapper;
template parameter(T): type of the referred element and
                        this can be  either function or object.

Example:

// C++ program to demonstrate the
// use of std::reference_wrapper
#include <iostream>
#include <functional>
using namespace std;

int main ()
{
    char a = 'g', b = 'e', c  = 'e', d = 'k', e = 's';

    // creating an array of character "references":
    reference_wrapper<char> ref[] = {a, b, c, d, e};

    for (char& s : ref)
          cout << s;

    return 0;
}

Output:

geeks