What does a BitWise OR (“|”) mean when used with a return statement?

Question

In C#.NET, has anyone ever seen a return statement inside a method that looks like this?

protected override Buttons GetButtonsToShow()
{
    return Buttons.New | Buttons.Return | Buttons.Delete;
}

How is this BitWise operator "|" working here? What is the result of this statement? I know how the BitWise operators work in if ... else ... statements and such, but I've never seen it used this way.

Answer 1

Buttons is a flags enum .

This makes it bit-mappable where you can use bitwise operators to combine values.

In this case it will returns a value that is a bitmap combining all of the three options.

This blog post has quite a clear explanation (though it uses & for the example).

Answer 2

Logically such methods return set of flags (the enum is marked with Flags attribute). Later you can check whether a certain flag is set using bitwise & .

In this particular example, somewhere there is code that checks whether to show a certain button. Something like this:

Buttons buttons = GetButtonsToShow();

bool showNewButton = (buttons & Buttons.New) != 0;

Answer 3

If you break down this expression it will become more clear:

protected override Buttons GetButtonsToShow()
{
    var returnValue = Buttons.New | Buttons.Return | Buttons.Delete;
    return returnValue;
}

Can you see it now?

The operator | does not alter the return statement itself. The result of the Buttons.New | Buttons.Return | Buttons.Delete Buttons.New | Buttons.Return | Buttons.Delete Buttons.New | Buttons.Return | Buttons.Delete expression is returned by the function.

Answer 4

It is performing the bitwise operations and using the result as the return value. Buttons is an enumeration that has the FlagsAttribute applied to it and looks something like the following:

[Flags]
public enum Buttons
{
    New = 1,
    Return = 2,
    Delete = 4
}

The usage of the return value from your GetButtonsToShow() method would be something like this:

private void DisplayButtons()
{
    var buttons = GetButtonsToShow(); // int value is 7, 1 + 2 + 4

    if ((buttons & Buttons.New) == Buttons.New) // if 7 (111) and 1 (001) equals 1 
    {
        buttonNew.Visible = true;
    }

    // above is for clarity, most likely all buttons visibility is set as:
    // buttonX.Visible = (buttons & Buttons.X) == Buttons.X;
}