DesignPatterns. Flyweight

“Приспособленец”. Если объект с такими признаками есть, в нашей коллекции, берем его, если нет, создаем. Работает совместно с фабрикой

program Flyweight;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,
  uFlyweight in 'uFlyweight.pas';

var
  bookFactory: TBookFactory;

begin
  bookFactory := TBookFactory.Create();
  try
    bookFactory.GetBookToRead('Alice in wonderland');
    bookFactory.GetBookToRead('Flying on Cooko''s nest');
    bookFactory.GetBookToRead('Delphi Cookbook');
    bookFactory.GetBookToRead('Delphi Cookbook');
    Readln;
  finally
    bookFactory.Free();
  end;
end.

Код шаблона “Приспособленец”

unit uFlyweight;

interface

uses
  System.Generics.Collections;

type
  TBook = class
  private
    FName: string;
  public
    constructor Create(aName: string);
  end;

  TBookFactory = class
    FBooksOnMyShelve: TDictionary<string, TBook>;
    function BuyNewBook(aName: string): TBook;
  public
    constructor Create();
    destructor Destroy; override;
    function GetBookToRead(aName: string): TBook;
  end;

implementation

{ TBookFactory }

function TBookFactory.BuyNewBook(aName: string): TBook;
begin
  Result := TBook.Create(aName);
end;

constructor TBookFactory.Create;
begin
  FBooksOnMyShelve := TDictionary<string, TBook>.Create();
end;

destructor TBookFactory.Destroy;
begin
  FBooksOnMyShelve.Free();
  inherited;
end;

function TBookFactory.GetBookToRead(aName: string): TBook;
begin
  if not FBooksOnMyShelve.TryGetValue(aName, Result) then
  begin
    FBooksOnMyShelve.Add(aName, BuyNewBook(aName));
    Writeln(aName + ' was bought');
  end
  else
    Writeln(aName + ' found on my shelve');
end;

{ TBook }

constructor TBook.Create(aName: string);
begin
  FName := aName;
end;

end.