Enum type constraints in C#
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Anyone know a good workaround for the lack of an enum generic constraint?
What is the reason behind C# not allowing type constraints on Enum 's? I'm sure there is a method behind the madness, but I'd like to understand why it's not possible.
Below is what I would like to be able to do (in theory).
public static T GetEnum<T>(this string description) where T : Enum
{
...
}
This is an occasionally requested feature.
As I'm fond of pointing out, ALL features are unimplemented until someone designs, specs, implements, tests, documents and ships the feature. So far, no one has done that for this one. There's no particularly unusual reason why not; we have lots of other things to do, limited budgets, and this one has never made it past the "wouldn't this be nice?" discussion in the language design team.
The CLR doesn't support it, so in order to make it work we'd need to do runtime work in addition to the language work. (see answer comments)
I can see that there are a few decent usage cases, but none of them are so compelling that we'd do this work rather than one of the hundreds of other features that are much more frequently requested, or have more compelling and farther-reaching usage cases. (If we're going to muck with this code, I'd personally prioritize delegate constraints way, way above enum constraints.)
Actually, it is possible, with an ugly trick. However, it cannot be used for extension methods.
public abstract class Enums<Temp> where Temp : class {
public static TEnum Parse<TEnum>(string name) where TEnum : struct, Temp {
return (TEnum)Enum.Parse(typeof(TEnum), name);
}
}
public abstract class Enums : Enums<Enum> { }
Enums.Parse<DateTimeKind>("Local")
If you want to, you can give Enums<Temp> a private constructor and a public nested abstract inherited class with Temp as Enum , to prevent inherited versions for non-enums.
Note that you can't use this trick to make extension methods.
public static T GetEnum<T>(this string description) where T : struct
{
return (T)Enum.Parse(typeof(T), description);
}
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