Vererbung und klassenspezifische Methoden

[Sir Rufo]

Und hier ein kleines Beispiel für die Verwendung von TPersistent

Delphi-Quellcode:

unit Unit2;

interface

uses
  System.Classes;

type
  TFoo = class abstract( TPersistent )
  protected
    procedure AssignTo( Dest: TPersistent ); override;
  public
    constructor Create( );
    constructor CreateFrom( Other: TFoo );
  end;

  TAdvancedFoo = class( TFoo )
  private
    FFirstName: string;
    procedure AssignTo( Other: TAdvancedFoo ); overload;
  protected
    procedure AssignTo( Dest: TPersistent ); overload; override;
  public
    property FirstName: string read FFirstName write FFirstName;
  end;

  TMoreAdvancedFoo = class( TAdvancedFoo )
  private
    FLastName: string;
    procedure AssignTo( Other: TMoreAdvancedFoo ); overload;
  protected
    procedure AssignTo( Dest: TPersistent ); overload; override;
  public
    property LastName: string read FLastName write FLastName;
  end;

implementation

{ TFoo }

procedure TFoo.AssignTo( Dest: TPersistent );
begin
  if Dest is TFoo
  then
  else
    inherited;
end;

constructor TFoo.Create;
begin
  inherited;
end;

constructor TFoo.CreateFrom( Other: TFoo );
begin
  Create;
  Self.Assign( Other );
end;

{ TAdvancedFoo }

procedure TAdvancedFoo.AssignTo( Dest: TPersistent );
begin
  inherited;
  if Dest is TAdvancedFoo
  then
    AssignTo( Dest as TAdvancedFoo );
end;

procedure TAdvancedFoo.AssignTo( Other: TAdvancedFoo );
begin
  Other.FFirstName := Self.FFirstName;
end;

{ TMoreAdvancedFoo }

procedure TMoreAdvancedFoo.AssignTo( Other: TMoreAdvancedFoo );
begin
  Other.FLastName := Self.FLastName;
end;

procedure TMoreAdvancedFoo.AssignTo( Dest: TPersistent );
begin
  inherited;
  if Dest is TMoreAdvancedFoo
  then
    AssignTo( Dest as TMoreAdvancedFoo );
end;

end.