Comments on: C# Enum Craziness: Sometimes What You Expect Isn’t The Case

By: Vipin Misys

Vipin Misys — Thu, 06 Nov 2008 08:59:39 +0000

Good Article.Does it mean that we can’t trust ENUM anymore

Thanks

By: Enums are Ints that Ain’t « Infovark Underground

Enums are Ints that Ain’t « Infovark Underground — Mon, 28 Jul 2008 14:42:35 +0000

[...] researching something to do with the new System.Addin namespace in C# 3.5, I was reminded of some enum craziness I’d [...]

By: Wöchentliche Rundablage: ASP.NET, ASP.NET MVC, System.AddIn, Silverlight, LINQ, C# 3.0, WPF, XBAP… | Code-Inside Blog

Mon, 04 Feb 2008 19:13:27 +0000

[...] C# Enum Craziness: Sometimes What You Expect Isn’t The Case [...]

By: NinjaCross

NinjaCross — Tue, 29 Jan 2008 10:47:24 +0000

It’s strange that no recommendations and specific hints are given in the official c# specs.
Anyway, I absolutely agree with the explanation made by James Curran.
Thanks Luke for pointing to this very important aspect of Enums

By: leppie

leppie — Tue, 29 Jan 2008 08:10:27 +0000

Enum.IsDefined() should be used.

By: Reflective Perspective - Chris Alcock » The Morning Brew #20

Reflective Perspective - Chris Alcock » The Morning Brew #20 — Tue, 29 Jan 2008 08:09:10 +0000

[...] C# Enum Craziness: Sometimes What You Expect Isn’t The Case « Spontaneous Publicity – Luke Foust talks about some of the stranger behaviour of the enum [...]

By: JohnB

JohnB — Tue, 29 Jan 2008 02:59:29 +0000

Interesting, I get the same results with VB too.

By: Justin Etheredge

Justin Etheredge — Tue, 29 Jan 2008 02:10:24 +0000

Another reason why this behavior can be useful is when it comes to extending enumerations. I came across this recently when working on a Linq provider where there is an ExpressionVisitor class that walks the expression tree. There is a framework enumeration that defines all of the possible expression types, but I can just as easy extend this visitor class to add several of my custom expression types. The ExpressionVisitor uses the enumeration from the framework and enumerations cannot be inherited from, but I can define my own enumeration and specify values that do not overlap with the framework enumeration. I can then pass in values from my new enumeration with no problems. Otherwise I would have to redefine the entire enumeration and add my custom values, then convert to the original enumeration when passing values to the base class. Whether or not this would be a better solution is up for debate.

By: James Curran

James Curran — Mon, 28 Jan 2008 23:57:28 +0000

[Flags] is part of it. The other part is that if the CLR had to verify every int to enum cast against EVERY possible enum value, your code would come to a screeching halt. Consider the code to handle that:

enum MyFlag myflag;
myflag = (int) someInt;

would become (effectively)

enum MyFlag myflag;
bool OK= false;
for(int v in Enum.GetValues(typeof(MyFlag))
{
if (v == someInt)
{
OK= true;
break;
}
if (!OK)
throw new InvalidCastException();

myflag = (int) someInt;

Do you really want to go through all that every time you assign an int to an enum? And remember, this cannot be done as compile time, even if the int being assigned is a constant, as the enum may be defined in a different assembly, and may change between compile & run.

By: Josh Tucholski

Josh Tucholski — Mon, 28 Jan 2008 20:08:32 +0000

I second their thoughts that this was meant for quick bit-masking. Take a look at the tutorial I wrote on flags with ASP.NET http://tucholski.blogspot.com/2007/10/dynamic-tab-navigation-wmaster-pages.html

By: Luke Foust

Luke Foust — Mon, 28 Jan 2008 18:51:33 +0000

I agree that OR-ing enums together is a feature (although it is rather un-intuitive). I with the compiler could make a distinction between enums which are marked with the [Flags] attribute and those which aren’t meant to be OR-ed together.

By: Will Sullivan

Will Sullivan — Mon, 28 Jan 2008 18:30:43 +0000

I believe the reason why this is possible is to support flags. In other words,

[flags()]
public enum MyFlag { unknown = 2, red = 4, blue = 8 }

public MyFlag WhoGotDaFlag = MyFlag.red | MyFlag.blue;

Test that out and see what the int value of WhoGotDaFlag is. I bet it isn’t 2, 4 or 8.

OR-ing together enum values is an extremely important feature of the CLR, and is used throughout the framework. I doubt it’ll be changed.