DesignPatterns. ChainOfResponsibilities

Есть цепочка объектов. Одно звено выполняет одни операции, другое – другие.

program ChainsOfResponsibilities;

{$APPTYPE CONSOLE}

{$R *.res}

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

var
  d: TDirector;
  m: TManager;
  w: TWorker;
  p: TPurchase;

begin
  d := TDirector.Create();
  m := TManager.Create();
  w := TWorker.Create();
  p := TPurchase.Create(5);
  try
    w.SetNextApprover(m);
    m.SetNextApprover(d);
    w.ProcessRequest(p); // trying to buy
    Readln;
  finally
    d.Free();
    m.Free();
    w.Free();
    p.Free();
  end;
end.

Шаблон “цепочки обязанностей”

unit uChainsOfResponsibilities;

interface

uses
  System.SysUtils;

type
  TPurchase = class
    FPrice: Double;
  public
    constructor Create(aPrice: Double);
    property Price: Double read FPrice;
  end;

  TApprover = class
    FNextApprover: TApprover;
  public
    procedure SetNextApprover(aApprover: TApprover);
    procedure ProcessRequest(aPurchase: TPurchase); virtual; abstract;
  end;

  TDirector = class(TApprover)
  public
    procedure ProcessRequest(aPurchase: TPurchase); override;
  end;

  TManager = class(TApprover)
  public
    procedure ProcessRequest(aPurchase: TPurchase); override;
  end;

  TWorker = class(TApprover)
  public
    procedure ProcessRequest(aPurchase: TPurchase); override;
  end;

implementation

{ TPurchase }

constructor TPurchase.Create(aPrice: Double);
begin
  FPrice := aPrice;
end;

{ TApprover }

procedure TApprover.SetNextApprover(aApprover: TApprover);
begin
  FNextApprover := aApprover;
end;

{ TDirector }

procedure TDirector.ProcessRequest(aPurchase: TPurchase);
begin
  if aPurchase.Price < 10 then
    Writeln('Director: approved')
  else
    Writeln('Director: too expensive');
end;

{ TManager }

procedure TManager.ProcessRequest(aPurchase: TPurchase);
begin
  if aPurchase.Price < 10 then
  begin
    Writeln('Manager: approved');
    FNextApprover.ProcessRequest(aPurchase);
  end
  else
    Writeln('Manage: too expensive');
end;

{ TWorker }

procedure TWorker.ProcessRequest(aPurchase: TPurchase);
begin
  if aPurchase.Price < 10 then
  begin
    Writeln('Worker: approved');
    FNextApprover.ProcessRequest(aPurchase);
  end
  else
    Writeln('Worker: too expensive');
end;

end.