TZblok

unit Singleton;

interface

type
  TSingleton = class sealed
  strict private
    class var FInstance: TSingleton;
  public
    // Global point of access to the unique instance
    class function Create: TSingleton;
    destructor Destroy; override;
  end;

implementation

{ TSingleton }

class function TSingleton.Create: TSingleton;
begin
  if FInstance = nil then
    FInstance := inherited Create as Self;
  Result := FInstance;
end;

destructor TSingleton.Destroy;
begin
  FInstance := nil;
  inherited;
end;

end.

Štítky: Delphi, Delphi programming, design patterns

Našel jsem ve Wikipedii (pro mě) podivný termín: Duck typing. Tak mě zajímalo co to je a jestli by to šlo implementovat v Delphi. Zde je výsledek:

/// This is example of duck typing in Delphi.
/// Based on: http://en.wikipedia.org/wiki/Duck_typing

program DuckTyping;

{$APPTYPE CONSOLE}

uses ObjComAuto;

{$METHODINFO ON} // important

type
  TDuck = class
  public
    procedure Quack;
    procedure Feathers;
  end;

  TPerson = class
  public
    procedure Quack;
    procedure Feathers;
  end;

procedure TDuck.Quack;
begin
  Writeln('Quaaaaaack!');
end;

procedure TDuck.Feathers;
begin
  Writeln('The duck has white and gray feathers.');
end;

procedure TPerson.Quack;
begin
  Writeln('The person imitates a duck.');
end;

procedure TPerson.Feathers;
begin
  Writeln('The person takes a feather from the ground and shows it.');
end;

procedure InTheForest(V: Variant);
begin
  V.Quack;
  V.Feathers;
end;

procedure Game;
var
  Duck, Person: Variant; // or IDispatch
begin
  Duck := TObjectDispatch.Create(TDuck.Create, True) as IDispatch;
  Person := TObjectDispatch.Create(TPerson.Create, True) as IDispatch;

  InTheForest(Duck);

  InTheForest(Person);
end;

begin
  Game;
end.

Štítky: Delphi, Delphi programming