在Delphi中具有继承性的流畅接口 [英] Fluent interface with inheritance in Delphi

问题描述

我有以下流利的接口声明和实现该接口的类：

I have following fluent interface declaration and class that implements that interface:

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;

我可以使用以下代码：

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

我必须通过添加 SaveToString 功能。

I have to extend above interface by adding SaveToString function.

我不想将该方法添加到原始的 IDocWriter 接口中，因为它不是所有接口的有效方法实现。所以我已经完成了

I don't want to add that method to original IDocWriter interface because it is not valid method for all interface implementations. So I have done following

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 IStrDocWriter 接口编写代码

var
  Writer: IDocWriter;
  s: string;

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

但是我希望能够使用它而无需声明 Writer 变量，类似于以下代码（当然不能编译）

But I would like to be able to use it without the need to declare Writer variable, something like following code (which, of course, cannot be compiled)

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

有什么方法可以实现？

Is there any way to achieve that?

可以对上述接口和类进行任何更改（显然，将这​​两个接口合并为一个）。

Any kind of changes to above interfaces and classes are acceptable (except, obviously, merging those two interfaces into one).

推荐答案

您可以这样写：

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

不，不是很好。流利的接口和继承这两个习惯用法根本就不混在一起。

No, not very nice is it. These two idioms, fluent interfaces and inheritance, simply do not mix.

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