How to capture a BitFlags type in a function parameter?

[realhet via Digitalmars-d-learn]

Hi,

I wan't to process every specialization of the BitFlags struct in 
a function:
So far the best I can come up is this:
  static void stdUI(F)(ref F flags) 
if(F.stringof.startsWith("BitFlags!(")){}

But it's obviously lame.
If I try this way:

  static void stdUI(E, U)(ref BitFlags!(E, U) flags){}

I get a cannot deduce arguments error.

Same error with:
  static void stdUI(E, U, B = BitFlags!(E, U))(ref B flags){}

I'd like to know the Enum type as well.

Thank You for your help in advance!