Question

Possible Duplicate:
Create Generic method constraining T to an Enum
Enum type constraints in C#

Consider the following class:

public class Transition<TState>
{
    public Transition ()
    {
        if (!typeof(TState).IsEnum)
            throw (new ArgumentException("[TState] has to be of type [System.Enum]."));
    }
}

Ideally, this should be declared as:

public class Transition<TState> where TState: System.Enum
{
}

The above, of course, generates a compile-time error. My question is why has that been made illegal. Most sources explain say that it is illegal but do not explain why. Any thoughts?

Answer 1

As Eric Lippert says that and I quote

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.”