Choice of variant record discriminant (design question)

[Jacob Sparre Andersen <sparre@nbi.dk>]

I have declared a record type like this:

   type Preprocessed_Parameters (Measurement_Count : Natural := 0) is
      record
         case Measurement_Count is
            when 0 =>
               null;
            when others =>
               Mean_Value      : Scalar;
               Scaled_Variance : Scalar;
         end case;
      end record;

I would like to return an object of that type from a function using
this piece of code:

   if Count = 0 then
      return (Measurement_Count => 0);
   else
      [...]
      return (Measurement_Count => Count,
              Mean_Value        => Mean,
              Scaled_Variance   => Sum);
   end if;

I can't do this, since the discriminant has to be static.  The obvious
solution to the problem is to change the record declaration into:

   type Preprocessed_Parameters (Empty : Boolean := True) is
      record
         case Empty is
            when True =>
               null;
            when False =>
               Measurement_Count : Positive;
               Mean_Value        : Scalar;
               Scaled_Variance   : Scalar;
         end case;
      end record;

but I have a feeling there ought to be a more elegant solution.  Does
somebody have a suggestion or two?

Jacob
-- 
ACRONYM: A Contrived Reduction Of Nomenclature Yielding Mnemonics