guideline

Use only simple aggregates when measured performance indicates.

   type Parent is tagged
      record
         C1 : Float;
         C2 : Float;
      end record;

   type Extension is new Parent with
      record
         C3 : Float;
         C4 : Float;
      end record;

   Parent_Var : Parent := (C1 => Float_Var1, C2 => Float_Var2);
   Exten_Var  : Extension;
   ...
   -- Simple aggregate
   -- (See ACES V2.0, test "a9_ob_simp_aggregate_02")
   Exten_Var := (C1 => Float_Var1, C2 => Float_Var2,
                 C3 => Float_Var3, C4 => Float_Var4);
   -- Extension aggregate
   -- (See ACES V2.0, test "a9_ob_ext_aggregate_02")
   Exten_Var := (Parent_Var with C3 => Float_Var3, C4 => Float_Var4);

rationale

Determine the impact of using extension aggregates. There may be a significant performance difference between evaluation of simple aggregates and evaluation of extension aggregates.