What type of parameter argument allows a pipe '|' in the arguments list? [duplicate]

Question

Possible Duplicate:
What does the bitwise or | operator do?

new Font(textBox1.Font, FontStyle.Bold | FontStyle.Italic);

What does the method signature that accepts this constructor call look like?

I never knew I could use the '|' operator in a method call. I would like to know more about it.

What is the English word for the '|' operator? (I don't even know how to google it as I do not know a word to describe it)

When it is used in a method, how do I explain it to another developer?

Would you recommend that I include this operator in my bag of tricks?

Does the operator have any special caveats?

Answer 1

The signature of the accepting method just looks like:

public Font(Font prototype, FontStyle newStyle)
{
    ...
}

The | operator (bitwise-or) in this context means that the font should be both bold and italic. It works like this because FontStyle is an enum decorated with a FlagsAttribute. The FontStyle definition is:

[Flags]
public enum FontStyle
{
    Bold = 1,
    Italic = 2,
    Regular = 0,
    Strikeout = 8,
    Underline = 4
}

So when you say FontStyle.Bold | FontStyle.Italic, it is bitwise-OR:

FontStyle.Bold                    = 1 = 00000001
FontStyle.Italic                  = 2 = 00000010
                                        ========
FontStyle.Bold | FontStyle.Italic = 3 = 00000011

Later, you can test the style parameter to see which bits are set using another bitwise operators (&). For example, if you want to see if the resulting style above is Bold, you can do:

FontStyle myStyle = FontStyle.Bold | FontStyle.Italic;
bool isBold = (myStyle & FontStyle.Bold) == FontStyle.Bold;

For example, the Bold property on the Font class checks if FontStyle.Bold was part of the style you gave it using almost the same code as above:

public bool Bold
{
    get
    {
        return ((this.Style & FontStyle.Bold) != FontStyle.Regular);
    }
}

Note that starting in .NET Framework 4 you could use Enum.HasFlag() to test the presence of a flag. For example, the above property definition could be reduced to (using a little syntactic sugar from C# 6):

public bool Bold => this.Style.HasFlag(FontStyle.Bold);