C#

static void Foo(ref string str) {
    str = "Yo";
}
 
static void Main(string[] args)
{
    string s = null;
    Foo(ref s);
    Console.WriteLine(s); // Will print "Yo" and not null
}

using System;
 
public class Test 
{
  public static void Main()
  {
    string s = string.Empty;
    Console.WriteLine(s);
 
    Foo(s);
    Console.WriteLine(s);
 
    Test t = new Test();
    Console.WriteLine(t.s);
 
    Foo(t);
    Console.WriteLine(t.s);
  }
  private static void Foo(string s)
  {
    s = "Testing";
  }
  private static void Foo(Test t)
  {
    t.s = "Testing";
  }
 
  public string s;
 
  public Test()
  {
    s = "This is a test";
  }
}

 
 
This is a test
Testing

public class MyClass
{
  private object o1;
  private object o2;
  public MyClass()
  {
  }
  public object O1
  {
    get { return this.o1; }
    set { this.o1 = value; }
  }
  public object O2
  {
    get { return this.o2; }
    set { this.o2 = value; }
  }
}