Is flags attribute necessary?

Question

I found with or without flags attributes, I can do bit operation if I defined the following enum

enum TestType
{
    None = 0x0,
    Type1 = 0x1,
    Type2 = 0x2
}

I am wondering why we need flags attribute?

possible duplicate of [Enum Flags Attribute](http://stackoverflow.com/questions/8447/enum-flags-attribute) — BoltClock, Feb 11 '11 at 10:28
Actually, I don't think it is a dupe; that dup doesn't *touch* on why it is needed; all of the examples there would work the same either way — Marc Gravell, Feb 11 '11 at 10:29
@Marc: Hmm, I just finished looking at some of the answers and you do have a point there. — BoltClock, Feb 11 '11 at 10:30

score 18 · Accepted Answer · answered Feb 11 '11 at 10:29

C# will treat them the same either way, but C# isn't the only consumer:

PropertyGrid will render it differently to allow combinations
XmlSerializer will accept / reject delimited combinations based on this flag
Enum.Parse likewise (from string), and the enum's .ToString() will behave differently
lots of other code that displays or processes the value will treat them differently

More importantly, though, it is an expression of intent to other developers (and code); this is meant to be treated as combinations, not exclusive values.

Possibly mention ToString, as a particularly common operation? — Jon Skeet, Feb 11 '11 at 10:30

score 1 · Answer 2 · answered Feb 11 '11 at 10:31

Sometimes bit combinations of enum values are meaningful (like FileAccess - read, write, read+write), sometimes they are not (usually). So [Flags] is descriptive way to store in metadata information that bit operations are meaningful on this enum type. There are several consumers of this attribute, for example ToString of that enum.

Is flags attribute necessary?

2 Answers2