Enums and validation

re: Enums and validation

jaybaz [MS] — Mon, 10 May 2004 23:16:00 GMT

"enums are not sets"

Enums aren't very OO, either. If you're worried about your enum getting used incorectly, force correct usage with OO programming techniques.

For example, check out
http://www.refactoring.com/catalog/replaceTypeCodeWithClass.html

http://www.refactoring.com/catalog/replaceTypeCodeWithStateStrategy.html

http://www.refactoring.com/catalog/replaceTypeCodeWithSubclasses.html

re: Enums and validation

ron — Mon, 10 May 2004 23:59:00 GMT

How can I use hyphens in enums? The following fails:

public enum CssTypes
{
background,
background-color,
background-image
}

thanks,
-ron

re: Enums and validation

Tomas Restrepo — Tue, 11 May 2004 00:13:00 GMT

Eric,

I'd actually change the default case in the switch to throw an exception (InvalidOperationException?), instead of just failing silently. That would make it much more easier to figure out what's going on...

re: Enums and validation

David M. Kean — Tue, 11 May 2004 02:07:00 GMT

or an InvalidEnumArgumentException...

re: Enums and validation

Robin Debreuil — Tue, 11 May 2004 04:53:00 GMT

One thing I find myself doing a lot with enums is having a default XX.Empty tag first (that acts as kind of a default 'null' value). Recently I've also been using 'End' tags too. The advantage is you can very quickly validate a tag (assuming you aren't using custom values) with a compare, like

Tag t = Tag.Open;
if(t > Tag.Empty && t < Tag.End){ // valid }

The main reason I went with this is I was having problems when inserting new values into the enum during development, it became a pain to hunt simple validation stuff down. When going to a new version, you can just add enums, and test for 'Tag.End2'.

Not sure if this is the best way though - it has yet to blow up in my face at least. I don't always like the idea of a value that is just used as a marker, it really should be a 'silent' value. I guess you could use .GetNames.Count or something code heavy like that. Of course switching to defined values would be painful...

I also usually throw an exception in the default switch clause (until release anyway!) when switching over an enum - just makes it easier to catch where the need to make a change after inserting a new value into an enum.

It would be great if the switch statement could be made to (optionally) throw an error when switching an enum and every case isn't explicitly covered.

re: Enums and validation

JosephCooney — Tue, 11 May 2004 06:09:00 GMT

I wrote an small entry on this a while ago too....
http://dotnetjunkies.com/WebLog/josephcooney/archive/2004/04/08/11002.aspx

Eric Gunnerson discusses Enums, Validation and Versioning...

Code/Tea/Etc... — Tue, 11 May 2004 10:04:00 GMT

re: Enums and validation

Todd Girvin — Tue, 11 May 2004 08:48:00 GMT

Eric, before giving your TechEd presentation, you might want to remove the extra commas in your enumerations. ;)

Great site

theDoctor .NET — Tue, 11 May 2004 12:00:00 GMT

re: Enums and validation

Jonathan Pryor — Tue, 11 May 2004 13:10:00 GMT

How do you use hyphens in enumeration values? You don't. The hyphen is not a valid character for identifiers.

The problem is that hypens, or anything "hyphen-like", such as non-breaking hyphen \u2011, figure dash \u2012, en dash \u2013, and minus sign \u2212, are all categorized as Pd (Punctuation, Dash).

Identifiers, in turn, can only contain characters from the Unicode categories Lu (Letter, uppercase), Ll (Letter, lowercase), Lt (Letter, Titlecase), Lm (Letter, Modifier), Lo (Letter, other), Mn (Mark, non-spacing), Me (Mark, enclosing), Pc (Punctuation, connecting), Cf (Other, format), Nd (Number, decimal digit), and Nl (Number, letter). Not necessarily in that order (numbers can't be the first character of an identifier).

The above is basically an i18n-aware version of the "standard" regex-like [_\w][_\d\w]+ pattern for identifiers.

In an ideal world, using @IDENTIFIER notation would save you, as prefixing an identifier with @ enables literal quoting, so you can have @bool to refer to a variable named 'bool'. However, the standard tokenizing rules also apply, so @one-two breaks down to the tokens {'one', '-', 'two'}, which doesn't work for you. If @IDENTIFIER included paranthesis for wrapping then you'd be fine saying @(one-two), allowing us to get all LISP-ish with our naming, but that wasn't done.

- Jon

re: Enums and validation

nfactorial — Tue, 11 May 2004 14:43:00 GMT

Todd, I see no extra commas in Eric's enumerations.

The trailing comma on the final entry is allowed and is also how I write my enumerations. Saving you having to add it when you want to add a new value!

Unless you meant something else, then I'm not sure what you mean :)

n!

re: Enums and validation

Jay Cook — Tue, 11 May 2004 21:56:00 GMT

I would try the following, use System.Enum.GetValues and then search the resulting array for a match. This will eliminate the hardcoded switch and if statements. For example,

using System;

namespace EnumExample
{
enum Operation
{
Fold,
Spindle,
Mutilate,
}

class Class1
{
static void Foo(Operation op)
{
int value = (int) op;
foreach(int i in Enum.GetValues(typeof(Operation)))
{
if (i == value)
{
Console.WriteLine(op.ToString() + " is a member of the enum");
return;
}
}

// not a member
Console.WriteLine(op.ToString() + " is not a member of the enum");
}

static void Main()
{
Foo(Operation.Fold);
Foo(Operation.Spindle);
Foo(Operation.Mutilate);
Foo((Operation) 42);
}
}
}

ViewState size, File Upload Memory Leak, Enums passed as Args and CancelEventArgs

ShowUsYour — Wed, 12 May 2004 02:05:00 GMT

ViewState size, File Upload Memory Leak, Enums passed as Args and CancelEventArgs

ShowUsYour — Wed, 12 May 2004 02:05:00 GMT

Using Enum in drop downs in a webform

DotWind Blog — Wed, 12 May 2004 10:05:00 GMT

re: Enums and validation

Tim — Wed, 12 May 2004 07:06:00 GMT

How about using strings in an enum I made a post about that after looking at your post. http://blog.dotwind.com/archive/2004/05/12/150.aspx
do you thing there is a way to do what I am trying there?

thanks

Using Enum in drop downs in a webform

DotWind Blog — Wed, 12 May 2004 10:21:00 GMT

re: Enums and validation

nfactorial — Wed, 12 May 2004 12:04:00 GMT

Tim,
In application I'm working on required similar functionality. However I wrote an attribute that could be applied to enum members to provide a 'display name' for the entry.

ie.

public enum MyEnum
{
[ EnumDisplayAttribute( "Some Example" )]
SomeExample,
}

This is a bit more work than it looks like you wanted (have to provide a customized combo-box as well) but works well.

Alternately, you could fake it by having a class with public, const strings:

public sealed class Example
{
private Example() {}

public const string Example = "An Example";
}

n!

re: Enums and validation

Thomas Eyde — Thu, 13 May 2004 00:58:00 GMT

How do you verify combinations like Fold + Spindle?

re: Enums and validation

Hugo Rodger-Brown — Thu, 13 May 2004 07:55:00 GMT

Thomas - you'd be looking to use bitwise logic to verify combinations of enums, for which you need to declare your attribute with the Flags attribute, see below for details:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemflagsattributeclasstopic.asp

re: Enums and validation

Tim — Thu, 13 May 2004 09:01:00 GMT

thanks n!

I love the idea of the attribute, I will definetly try that.

the const strings class is the way I have been doing it. I just found it really easy to bind the enum to the combo box and also to store the values in the database instead of having a different table with the categories I will just put it as an enum and store the int value for it in the table.

Tim

MBA

MBA — Sat, 18 Dec 2004 18:51:00 GMT

Helpful For MBA Fans.

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