Different behaviours in cast operations?

Question

Could anyone please explain to me why ,in those two casting scenarios below, the casted variables acts different? While first variable (double initial) preserves its initial value in the first example code, the "sender" object changes its content property value according to the new variable which it was casted into?

1st ex:

double initialValue = 5;

int secValue = (int)initial;

secValue = 10;

Console.WriteLine(initial); // initial value is still 5.

2nd ex:

private void Button_Click(object sender, RoutedEventArgs e)
{
    Button btn = (Button)sender;
    btn.Content = "Clicked"; // "sender" objects content property is also set to "Clicked".
}

Because `int` is a value-type and `Button` is a reference-type. See https://msdn.microsoft.com/en-us/library/t63sy5hs.aspx — haim770, May 17 '15 at 11:49

score 4 · Accepted Answer · edited May 23 '17 at 10:26

This has nothing to do with casting. This is the difference between value types and reference types. int is a value type, Button is a reference type:

int a = 1;
int b = a;  // the value of a is *copied* to b

Button btnA = ...;
Button btnB = btnA;  // both `btnA` and `btnB` point to the *same* object.

Simply speaking, value types contain a value, reference types refer to some object. Illustration:

  a       b      btnA     btnB
+---+   +---+     |        |
| 1 |   | 1 |     |        +---------+
+---+   +---+     |                  v
                  |             +-------------+
                  +-----------> |  The button |
                                +-------------+

The following question contains a more details explanation of this issue:

What is the difference between a reference type and value type in c#?

Note, though, that in your first example, you are reassigning the value of secValue. You can do the same for reference types as well:

b = 2;
btnB = someOtherButton;

  a       b      btnA     btnB
+---+   +---+     |        |              +-------------------+
| 1 |   | 2 |     |        +------------> | Some other button |
+---+   +---+     |                       +-------------------+
                  |     +-------------+
                  +---> |  The button |
                        +-------------+

In your second example, you are simply modifying a property of the button, you are not changing which object the variable points to.

Value types doesn't really matter here. OP is re-assigning the variable; not mutating it(in first example). Even if it were a referencetype, it will behave the same. — Sriram Sakthivel, May 17 '15 at 11:55
@SriramSakthivel But the OP is assuming reference semantics on a value type as well. — Yuval Itzchakov, May 17 '15 at 11:56
@SriramSakthivel: Thanks for the feed-back, I've incorporated it into my answer (and +1 to yours). — Heinzi, May 17 '15 at 12:00
@YuvalItzchakov I don't see it. But simply this question doesn't makes much sense. — Sriram Sakthivel, May 17 '15 at 12:14

Different behaviours in cast operations?

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