Why does std::is_const::value evaluate to false?

Question

This is a spin off of the question How to check if object is const or not?.

I was surprised to see the following program

#include 
#i         


        

Answer 1

A const qualifier on a reference just means that the value can't be modified via the reference. It can still be modified by other means. For example:

int a = 1;
const int &b = a;

std::cout << b << std::endl;  // Prints 1

a = 2;

std::cout << b << std::endl;  // Prints 2

Thus, you can't assume that the value of a const reference is actually constant.