Best way to implement fluent extension on the enum member

Question

Lets say I got the extension which does something with the enum and then just returns it.

public static T Do<T>(this Enum e) where T : struct
{
    // Do something.
    return // e? .. (T)e? .. or (T)(object)e? ;
}

So what should I return to let my code be successefully built and run with this example:

Roles role = Roles.Admin | Roles.Moderator;
role.Do<Roles>().SomethingElse().AndMore<Roles>().Etc<int>();

__

return (T)e;

__

return e;

__

return (T)(object)e;

Actually works, but does boxing and then unboxing.

What is your specific problem? Adding more extension methods should not be the problem. — Felix K., Oct 08 '12 at 08:40
How is the `SomethingElse` method defined? What type does it expect to operate upon? — Darin Dimitrov, Oct 08 '12 at 08:44
@DarinDimitrov that's not the point. The point is in the `Do` method. — AgentFire, Oct 08 '12 at 08:44
@AgentFire, of course that it is the point. You have to return the type that the next function in the chain expects. — Darin Dimitrov, Oct 08 '12 at 08:45
@DarinDimitrov I have to return the type I have received as an input. So I am asking the best way to do that. — AgentFire, Oct 08 '12 at 08:45
@AgentFire Then remove the generic parameter and return the enum type.... — Felix K., Oct 08 '12 at 08:47
@AgentFire Just as a note, the `Enum` *class* will cause boxing of arguments in your sample above. There isn't an easy way to get constraints on `enum` types, but [Jon Skeet has some code exploring the area](http://code.google.com/p/unconstrained-melody/). — Adam Houldsworth, Oct 08 '12 at 08:47
@FelixK. in that case I will lose the desirable return type (`Roles` or whatever). — AgentFire, Oct 08 '12 at 08:49
Just for your information: http://stackoverflow.com/questions/79126/create-generic-method-constraining-t-to-an-enum — sloth, Oct 08 '12 at 08:52

score 1 · Accepted Answer · answered Oct 08 '12 at 08:48

1

    public static T Do<T>(this Enum e) where T : struct
    {
        return (T) Convert.ChangeType(e, typeof(T));
    }

answered Oct 08 '12 at 08:48

1

Still, boxing **and** then unboxing. – AgentFire Oct 08 '12 at 08:49
1

@AgentFire The boxing will occur because of your use of `Enum`. – Adam Houldsworth Oct 08 '12 at 08:52

score 1 · Answer 2 · answered Oct 08 '12 at 08:51

This is a tricky one due to the fact that you can't place an Enum constraint on a generic.

Have a look at this article for more, and a possible workaround:

score 0 · Answer 3 · answered Oct 08 '12 at 08:41

0

Well you have to obey the mathematical construct of Closure.
Wikipedia explaines this well: Closrue

In a short sentence:
In your case you have to return what your next functions exprects as input parameter.

answered Oct 08 '12 at 08:41

TGlatzer

3 Answers3