C++ Difference between std::ref(T) and T&?

Question

I have some questions regarding this program:

#include 
#include 
#include 
using namespace std;
template &l         


        

Answer 1

std::reference_wrapper is recognized by standard facilities to be able to pass objects by reference in pass-by-value contexts.

For example, std::bind can take in the std::ref() to something, transmit it by value, and unpacks it back into a reference later on.

void print(int i) {
    std::cout << i << '\n';
}

int main() {
    int i = 10;

    auto f1 = std::bind(print, i);
    auto f2 = std::bind(print, std::ref(i));

    i = 20;

    f1();
    f2();
}

This snippet outputs :

10
20

The value of i has been stored (taken by value) into f1 at the point it was initialized, but f2 has kept an std::reference_wrapper by value, and thus behaves like it took in an int&.