Pattern "chain of duties"

[carriann]

How do you put it in delphi?

[Analeea]

You can read the patter in the book. http://www.ozon.ru/context/detail/id/2457392/ or that http://codelib.ru/pattern/chain_of_responsibility/ who, in fact, duplicates information from the relevant book.

---

From the more adequate realities of nations Delphi The most understandable is:

unit Pattern;
interface
uses SysUtils;
type
TPurchase = class

public

Number: integer;

Amount: Double;

Purpose: string;

constructor Create(num: integer; am: Double; pur: string);

end;
IApprover = interface

['{3ACA3967-FFCF-48A1-AC45-9A9B98A8DD96}']

procedure SetSuccessor(successor: IApprover);

procedure ProcessRequest(purchase: TPurchase);

end;
TApprover = class(TInterfacedObject, IApprover)

protected

FSuccessor: IApprover;

public

procedure SetSuccessor(successor: IApprover);

procedure ProcessRequest(purchase: TPurchase); virtual; abstract;

end;
TDirector = class(TApprover)

procedure ProcessRequest(purchase: TPurchase); override;

end;
TVicePresident = class(TApprover)

procedure ProcessRequest(purchase: TPurchase); override;

end;
TPresident = class(TApprover)

procedure ProcessRequest(purchase: TPurchase); override;

end;
implementation
{ TApprover }
procedure TApprover.SetSuccessor(successor: IApprover);

begin

FSuccessor := successor;

end;
{ TDirector }
procedure TDirector.ProcessRequest(purchase: TPurchase);

begin

if purchase.Amount < 10000.0 then

WriteLn(Format('Director approved request # %d', [purchase.Number]))

else if FSuccessor  nil then

FSuccessor.ProcessRequest(purchase);

end;
{ TVicePresident }
procedure TVicePresident.ProcessRequest(purchase: TPurchase);

begin

if purchase.Amount < 25000.0 then

WriteLn(Format('VicePresident approved request # %d', [purchase.Number]))

else if FSuccessor  nil then

FSuccessor.ProcessRequest(purchase);

end;
{ TPresident }
procedure TPresident.ProcessRequest(purchase: TPurchase);

begin

if purchase.Amount < 100000.0 then

WriteLn(Format('President approved request # %d', [purchase.Number]))

else

WriteLn(Format('Request# %d requires an executive meeting!', [purchase.Number]))

end;
{ TPurchase }
constructor TPurchase.Create(num: integer; am: Double; pur: string);

begin

Number := num;

Amount := am;

Purpose := pur;

end;
end.

---

program Behavioral.ChainOfResponsibility.Pattern;

{$APPTYPE CONSOLE}
uses

SysUtils,

Pattern in 'Pattern.pas';
var

Director: IApprover;

VicePresident: IApprover;

President: IApprover;

Purchase: TPurchase;
begin

ReportMemoryLeaksOnShutDown := DebugHook <> 0;

try

Director := TDirector.Create;

VicePresident := TVicePresident.Create;

President := TPresident.Create;
try
  Director.SetSuccessor(VicePresident);
  VicePresident.SetSuccessor(President);

  Purchase := TPurchase.Create(2034, 350.00, 'Supplies');
  Director.ProcessRequest(Purchase);

  Purchase.Free;
  Purchase := TPurchase.Create(2035, 32590.10, 'Project X');
  Director.ProcessRequest(Purchase);

  Purchase.Free;
  Purchase := TPurchase.Create(2036, 122100.00, 'Project Y');
  Director.ProcessRequest(Purchase);

  ReadLn;
finally
  Purchase.Free;
end;

except

on E:Exception do

Writeln(E.Classname, ': ', E.Message);

end;

end.