This is an excerpt from the C# Language Specification. Enums are value types and there is no way that you can specify the System.ValueType as a constraint, as per the specification. But if you wish to specify a non-reference type as a [primary] constraint, struct can be used.
private void Method
That does not guarantee that our generic method will not accept other value types, besides enum, for which we do not support our functionality.
During the course of investigation, I was extremely surprised to know that the numeric types like int, float etc in C# are struct. It is not far from the fact that they are value types, but it was interesting to know that they are declared as
public struct Int32 : IComparable, IFormattable, IConvertible, IComparable
Similar thing for other numeric types. Whereas an enum [System.Enum], though a value type, is declared as an abstract class that derives from System.ValueTypes unlike the int or float. The end result is that enums are value types but i wonder the way they are declared.
Anyway, the question still remains unresolved - why enums cannot be used as constraints, andjust the specification saying that enums cannot be used as constraints is unsatisfactory.
I am not sure if there is any other way to resolve my situation.
Refer section 25.7 through for the specification on Generic Type Constraints.