Click here to Skip to main content
11,702,981 members (60,206 online)
Click here to Skip to main content

Generic type restriction for enums

, 10 Jul 2011 LGPL3 9.1K 6
Rate this:
Please Sign up or sign in to vote.
How to restrict a generic type identifier to only allow enums.

I was looking for a way to restrict a generic type identifier to only allow enums. Since you are not allowed to use where T : Enum, I checked the metadata for Enum and found that it implements ValueType, IComparable, IFormattable, IConvertible. You can't use ValueType as restriction, but struct works fine.

In other words, use “where T : struct, IComparable, IFormattable, IConvertible” to make a type restriction which should work well as an enum restriction.

The reason why I needed the specification is that I want to be able to fetch the DescriptionAttribute from enums. I use it to be able to add friendly names to enum values.

Example enum:

public enum MyEnum
{
    [Description("Some value"]
    SomeValue,

    [Description("Foo bar")]
    FooBar
}

Fetch value:

MyEnum value = MyEnum.FooBar;

// will display "Foo bar"
Console.WriteLine(value.GetDescription());

The extension method that does the magic:

public static string GetDescription<T>(this T instance)
    where T : struct, IConvertible, IFormattable, IComparable
{
    var type = typeof (T);
    var memberInfo = type.GetMember(instance.ToString())[0];

    var attribute = (DescriptionAttribute)memberInfo.GetCustomAttributes(
        typeof(DescriptionAttribute), false).FirstOrDefault();
    return attribute == null ? instance.ToString() : attribute.Description;
}

License

This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)

Share

About the Author

jgauffin
Founder Gauffin Interactive AB
Sweden Sweden
Founder of OneTrueError, a .NET service which captures, analyzes and provide possible solutions for exceptions.

blog | twitter

You may also be interested in...

Comments and Discussions

 
GeneralMy vote of 3 Pin
Richard Deeming13-Jul-11 8:20
memberRichard Deeming13-Jul-11 8:20 
Suggestionnicely done Pin
IGood12-Jul-11 8:02
memberIGood12-Jul-11 8:02 
GeneralRe: nicely done Pin
jgauffin12-Jul-11 19:34
memberjgauffin12-Jul-11 19:34 
GeneralRe: nicely done Pin
IGood13-Jul-11 16:33
memberIGood13-Jul-11 16:33 
GeneralRe: nicely done Pin
jgauffin13-Jul-11 19:43
memberjgauffin13-Jul-11 19:43 
GeneralRe: nicely done Pin
IGood14-Jul-11 6:49
memberIGood14-Jul-11 6:49 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web03 | 2.8.150819.1 | Last Updated 10 Jul 2011
Article Copyright 2011 by jgauffin
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid