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This causes a compile-time exception:
public sealed class ValidatesAttribute<T> : Attribute { } [Validates<string>] public static class StringValidation { } I realize C# does not support generic attributes. However, after much Googling, I can’t seem to find the reason.
Does anyone know why generic types cannot derive from Attribute? Any theories?
Well, I can’t answer why it’s not available, but I can confirm that it’s not a CLI issue. The CLI spec doesn’t mention it (as far as I can see) and if you use IL directly you can create a generic attribute. The part of the C# 3 spec that bans it – section 10.1.4 ‘Class base specification’ doesn’t give any justification.
The annotated ECMA C# 2 spec doesn’t give any helpful information either, although it does provide an example of what’s not allowed.
My copy of the annotated C# 3 spec should arrive tomorrow… I’ll see if that gives any more information. Anyway, it’s definitely a language decision rather than a runtime one.
EDIT: Answer from Eric Lippert (paraphrased): no particular reason, except to avoid complexity in both the language and compiler for a use case which doesn’t add much value.