enum subsets?

[bearophile]

I'd like to define an enum type with only a subset of the fields 
of another enum.

enum Foo { A, B, C }
enum Bar : Foo { Foo.A, Foo.B }
void main() {
     //Foo f = Bar.A; // Should be OK.
     //Bar b = Foo.A; // Should be an error.
}


I receive the errors:

temp.d(2): Error: type only allowed if anonymous enum and no enum 
type
temp.d(2): Error: if type, there must be an initializer
temp.d(2): Error: type only allowed if anonymous enum and no enum 
type
temp.d(2): Error: if type, there must be an initializer


Defining a subset like that is quite useful, it allows to 
statically avoid some bugs.

An alternative and more clear syntax:

enum Foo { A, B, C }
subset enum Bar : Foo { A, B }
superset enum Spam : Foo { D }
void main() {}


Perhaps something like that can be implemented with Phobos 
library code (with a worse syntax)?

Bye,
bearophile