In C++, passing const references is a common practice - for instance :

#include <iostream>
using namespace std;

class X
{
  public :
    X()                              {m_x = 0; }
    X(const int & x)                 {m_x = x; }
    X(const X & other)               { *this = other; }
    X & operator = (const X & other) { m_x = other.m_x; return *this; }
    void print()                     { cout << m_x << endl; }
  private :
    int m_x;
};

void main()
{
    X x1(5);
    X x2(4);
    X x3(x2);
    x2 = x1;
    x1.print();
    x2.print();
    x3.print();
}

This very simple example illustrates how it's done - pretty much. However I've noticed that in C# this doesn't seem to be the case. Do I have to pass const references in C# ? what do I need the "ref" keyword for? Please note that I know and understand what C# reference and value types are.