unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  end;

  IMyInterface1 = interface
    function Func(a,b: Integer): Integer;
  end;

  TAdd = class(TInterfacedObject, IMyInterface1)
  public
    function Func(a: Integer; b: Integer): Integer;
    destructor Destroy; override;
  end;

  TMul = class(TInterfacedObject, IMyInterface1)
  public
    function Func(a: Integer; b: Integer): Integer;
    destructor Destroy; override;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TAdd }

destructor TAdd.Destroy;
begin
  ShowMessage('TAdd.Destroy');
  inherited;
end;

function TAdd.Func(a, b: Integer): Integer;
begin
  Result := a + b;
end;

{ TMul }

destructor TMul.Destroy;
begin
  ShowMessage('TMul.Destroy');
  inherited;
end;

function TMul.Func(a, b: Integer): Integer;
begin
  Result := a * b;
end;

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
var
  I: IMyInterface1;
begin
  I := TAdd.Create;
  ShowMessage(IntToStr(I.Func(9, 9))); {18}

  I := TMul.Create;  {I 在指向新的目标前会先释放前面所属的类}
  ShowMessage(IntToStr(I.Func(9, 9))); {81}
end;

end.