Наследование и виртуальные методы

// Отделите правило языка от удачного запуска VirtualDispatch.
program VirtualDispatch;
{$APPTYPE CONSOLE}
type
  TBase = class
    procedure Print; virtual;
  end;
  TChild = class(TBase)
    procedure Print; override;
  end;
procedure TBase.Print;
begin Writeln('base'); end;
procedure TChild.Print;
begin Writeln('child'); end;
var
  X: TBase;
begin
  X := TChild.Create;
  try X.Print; finally X.Free; end;
end.

// Определите реальную гарантию в Polymorphism.
program Polymorphism;
{$APPTYPE CONSOLE}
type
  TShape = class
    function Area: Double; virtual; abstract;
  end;
  TSquare = class(TShape)
    Side: Double;
    function Area: Double; override;
  end;
function TSquare.Area: Double;
begin Result := Side * Side; end;
var
  Shape: TShape;
begin
  Shape := TSquare.Create;
  try
    TSquare(Shape).Side := 3;
    Writeln(Shape.Area:0:1);
  finally Shape.Free; end;
end.

// Отделите правило языка от удачного запуска InheritedOrder.
program InheritedOrder;
{$APPTYPE CONSOLE}
type
  TBase = class
    procedure Save; virtual;
  end;
  TChild = class(TBase)
    procedure Save; override;
  end;
procedure TBase.Save;
begin Writeln('base save'); end;
procedure TChild.Save;
begin
  Writeln('validate');
  inherited;
  Writeln('notify');
end;
begin end.

// Проследите фактическое поведение AbstractDemo.
program AbstractDemo;
{$APPTYPE CONSOLE}
uses System.SysUtils;
type
  TFormatter = class abstract
    function Format(N: Integer): string; virtual; abstract;
  end;
  THexFormatter = class(TFormatter)
    function Format(N: Integer): string; override;
  end;
function THexFormatter.Format(N: Integer): string;
begin
  Result := IntToHex(N, 1);
end;
begin end.