uses System.Reflection;

type MyClass = class
private
  x: integer := 5;
public
  procedure PrintFields := Print(x);
end;

begin
  var a := new MyClass;
  var fi := a.GetType.GetField('x', BindingFlags.Instance or BindingFlags.NonPublic);
  fi.SetValue(a,777);
  a.PrintFields;
end.