C#

FormX objX = new FormX();

// cast down
Form obj = objX;

// now you can call the foo method
foo(ref obj);

foo(System.Windows.Forms.Form obj)
{
    // obj is passed as a reference by default since it's a reference type
}

Member 2463256 wrote:

However, since FormX is a reference type, your foo method doesn't even need the ref parameter keyword. c# passes it as a reference by default.

foo(ref Form obj)
{
  // The caller's variable is changed to a new
  // Form instance.
  obj = new Form();
}

foo(Form obj)
{
  // Our LOCAL variable 'obj' is set to a new form, but
  // the calling function will see no change.
  obj = new Form();
}

Ian Shlasko wrote:

except that "out" only works in one direction, while "ref" both provides a value and allows it to be changed.

// Notice myForm was not initialized.
Form myForm;
SomeMethod(out myForm);
// This will work.
myForm.ShowDialog();

// Notice myForm was not initialized.
Form myForm;
SomeMethod(ref myForm);
// This will NOT work (compile time error), because myForm may not have been initialized.
myForm.ShowDialog();