delphi - Delphi 中具有继承性的流畅界面

Question

我有以下流畅的接口(interface)声明和实现该接口(interface)的类:

type
  IDocWriter = interface
    ['{8CB5799A-14B1-4287-92FD-41561B237560}']
    function Open: IDocWriter;
    function Close: IDocWriter;
    function Add(const s: string): IDocWriter;
    function SaveToStream(Stream: TStream): IDocWriter;
  end;

  TDocWriter = class(TInterfacedObject, IDocWriter)
  public
    function Open: IDocWriter;
    function Close: IDocWriter;
    function Add(const s: string): IDocWriter;
    function SaveToStream(Stream: TStream): IDocWriter;
  end;

{ TDocWriter }

function TDocWriter.Open: IDocWriter;
begin
  Result := Self;
  // DoOpen
end;

function TDocWriter.Close: IDocWriter;
begin
  Result := Self;
  // DoClose
end;

function TDocWriter.Add(const s: string): IDocWriter;
begin
  Result := Self;
  // DoAdd
end;

function TDocWriter.SaveToStream(Stream: TStream): IDocWriter;
begin
  Result := Self;
  // DoSaveToStream
end;

我可以像这样使用上面的代码:

var
  Stream: TStream;
  ...
  TDocWriter.Create
    .Open
    .Add('abc')
    .Close
    .SaveToStream(Stream);

我必须通过添加 SaveToString 函数来扩展上面的接口(interface)。

我不想将该方法添加到原始 IDocWriter 接口(interface)中，因为它不是对所有接口(interface)实现都有效的方法。所以我做了以下工作

type
  IStrDocWriter = interface(IDocWriter)
    ['{177A0D1A-156A-4606-B594-E6D20818CE51}']
    function SaveToString: string;
  end;

  TStrDocWriter = class(TDocWriter, IStrDocWriter)
  public
    function SaveToString: string;
  end;

{ TStrDocWriter }

function TStrDocWriter.SaveToString: string;
begin
  Result := 'DoSaveToString';
end;

为了使用ISrDocWriter接口(interface)，我必须编写代码

var
  Writer: IDocWriter;
  s: string;

  Writer := TStrDocWriter.Create
    .Open
    .Add('abc')
    .Close;
  s := (Writer as IStrDocWriter).SaveToString;

但我希望能够使用它而无需声明 Writer 变量，例如以下代码(当然，无法编译)

  s := TStrDocWriter.Create
    .Open
    .Add('abc')
    .Close
    .SaveToString;   // Undeclared identifier SaveToString

有什么办法可以实现吗？

对上述接口(interface)和类的任何类型的更改都是可以接受的(显然，除了将这两个接口(interface)合并为一个之外)。

Answer 1

你可以这样写:

s := (TStrDocWriter.Create
    .Open
    .Add('abc')
    .Close as IStrDocWriter)
    .SaveToString; 

不，不是很好。流畅的接口(interface)和继承这两个习惯用法根本不能混合。