DesignPatterns. Builder

Паттерн строитель

Когда необходимо создать объект (TProduct) из разных блоков. Разные строители (TConcreteBuilder) могут использовать разные технологии.

Main

program Builder;

{$APPTYPE CONSOLE}

{$R *.res}

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

var
  b: TBuilder;
  d: TDirector;
  p: TProduct;

begin
  try
    b := TConcreteBuilder.Create();
    d := TDirector.Create(b);
    try
      p := d.Construct();
      Writeln('done');
      Readln;
    finally
      b.Free();
      d.Free();
      p.Free();
    end;

  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Модуль uBuilder

unit uBuilder;

interface

uses
  System.Generics.Collections, System.SysUtils;

type
  TProduct = class
  private
    FParts: TObjectList<TObject>;
  public
    constructor Create();
    destructor Destroy; override;
    procedure Add(aPart: TObject);
  end;

  TBuilder = class
  public
    procedure BuldPartA(); virtual; abstract;
    procedure BuldPartB(); virtual; abstract;
    procedure BuldPartC(); virtual; abstract;
    function GetProduct(): TProduct; virtual; abstract;
  end;

  TConcreteBuilder = class(TBuilder)
  private
    FProduct: TProduct;
  public
    constructor Create();
    destructor Destroy; override;
    procedure BuldPartA(); override;
    procedure BuldPartB(); override;
    procedure BuldPartC(); override;
    function GetProduct(): TProduct; override;
  end;

type
  TDirector = class
  private
    FBuilder: TBuilder;
  public
    constructor Create(aBuilder: TBuilder);
    destructor Destroy; override;
    function Construct(): TProduct;
  end;

implementation

{ TDirector }

function TDirector.Construct: TProduct;
begin
  FBuilder.BuldPartA();
  FBuilder.BuldPartB();
  FBuilder.BuldPartC();
  Result := FBuilder.GetProduct();
end;

constructor TDirector.Create(aBuilder: TBuilder);
begin
  FBuilder := TConcreteBuilder.Create();
end;

destructor TDirector.Destroy;
begin
  FBuilder.Free();
  inherited;
end;

{ TProduct }

procedure TProduct.Add(aPart: TObject);
begin
  FParts.Add(aPart);
end;

constructor TProduct.Create;
begin
  FParts := TObjectList<TObject>.Create(true);
end;

destructor TProduct.Destroy;
begin
  FParts.Free();
  inherited;
end;

{ TConcreteBuilder }

procedure TConcreteBuilder.BuldPartA;
var
  s: string;
begin
  s := 'partA';
  FProduct.Add(TObject(s));
end;

procedure TConcreteBuilder.BuldPartB;
var
  s: string;
begin
  s := 'partB';
  FProduct.Add(TObject(s));
end;

procedure TConcreteBuilder.BuldPartC;
var
  s: string;
begin
  s := 'partC';
  FProduct.Add(TObject(s));
end;

constructor TConcreteBuilder.Create;
begin
  FProduct := TProduct.Create();
end;

destructor TConcreteBuilder.Destroy;
begin
  FProduct.Free();
  inherited;
end;

function TConcreteBuilder.GetProduct: TProduct;
begin
  Result := FProduct;
end;

end.