9.1. Discriminants - JulTob/Ada GitHub Wiki

Derived types can be parametrized with the use of discriminants.

They can also determine the type of object.

type Buffer (Length:Positive) is record
   Buff:String(1..Length); 
end record;

type Vehicle (IsFast: Boolean; Kind :VehicleKind) is record
   FastLane: Boolean := IsFast;
   case Kind is
      when Car =>
         Full : Boolean;
      when Truck=>
         Weight: Positive;
end record;

type Major_Type is (Letters, Sciences);
type Grade is delta 0.01 range 00.00 .. 10.00;
type Student (Major : Major_Type; Name_Length: Positive)
is record
  Name : String(1..Name_Length);
  Maths : Grade;
  Philosophy: Grade;
  English : Grade;
  case Major is
    when Letters =>
      Latin : Grade;
      French: Grade;
    when Sciences =>
      Biology : Grade;
      Physics : Grade;
   end case;
end record; 

Discriminants cannot change during the life of the object.