鸭子在 Delphi 2007 中打字? [英] Duck typing in Delphi 2007?

问题描述

问题:

有没有办法用 Delphi 2007 做鸭子输入(即没有泛型和高级 Rtti 功能)?

Is there a way to do duck typing with Delphi 2007 (i.e. without generics and advanced Rtti features)?

Delphi 2010 以后的鸭子打字资源:

• Duck Duck Delphi 由 ARCANA.
• Delphi 中的鸭子打字 作者 Daniele Teti.
• AOP 和 Delphi 中的鸭子输入 来自 Stefan Glienke.

• Duck Duck Delphi in google project by ARCANA.
• Duck Typing in Delphi by Daniele Teti.
• AOP and duck typing in Delphi by Stefan Glienke.

上次

我深入研究了上面列出的资源，并研究了这里发布的每个答案.

I've delved more into the resouces listed above and studied every posted answers here.

我最终完善了我的要求并做了一个后续帖子这个问题.

I end up refining my requirement a made a follow up post to this question.

推荐答案

在 ObjAuto.pas 和可调用的变体类型的帮助下，这应该是可能的(用 XE 编写，但也应该在 Delphi 7 或更低版本中运行):

With the help of the ObjAuto.pas and invokable variant types it should be possible (written in XE but should also run in Delphi 7 or lower):

unit DuckTyping;

interface

function Duck(Instance: TObject): Variant;

implementation

uses
  ObjAuto,
  SysUtils,
  TypInfo,
  Variants;

type
  TDuckVarData = packed record
    VType: TVarType;
    Reserved1, Reserved2, Reserved3: Word;
    VDuck: TObject;
    Reserved4: LongWord;
  end;

  TDuckVariantType = class(TPublishableVariantType)
  protected
    function GetInstance(const V: TVarData): TObject; override;
  public
    procedure Clear(var V: TVarData); override;
    procedure Copy(var Dest: TVarData; const Source: TVarData;
      const Indirect: Boolean); override;
    function DoFunction(var Dest: TVarData; const V: TVarData;
      const Name: string; const Arguments: TVarDataArray): Boolean; override;
  end;

var
  DuckVariantType: TDuckVariantType;

{ TDuckVariantType }

procedure TDuckVariantType.Clear(var V: TVarData);
begin
  V.VType := varEmpty;
  TDuckVarData(V).VDuck := nil;
end;

procedure TDuckVariantType.Copy(var Dest: TVarData; const Source: TVarData;
  const Indirect: Boolean);
begin
  if Indirect and VarDataIsByRef(Source) then
    VarDataCopyNoInd(Dest, Source)
  else
  begin
    with TDuckVarData(Dest) do
    begin
      VType := VarType;
      VDuck := TDuckVarData(Source).VDuck;
    end;
  end;
end;

function TDuckVariantType.DoFunction(var Dest: TVarData; const V: TVarData;
  const Name: string; const Arguments: TVarDataArray): Boolean;
var
  instance: TObject;
  methodInfo: PMethodInfoHeader;
  paramIndexes: array of Integer;
  params: array of Variant;
  i: Integer;
  ReturnValue: Variant;
begin
  instance := GetInstance(V);
  methodInfo := GetMethodInfo(instance, ShortString(Name));
  Result := Assigned(methodInfo);
  if Result then
  begin
    SetLength(paramIndexes, Length(Arguments));
    SetLength(params, Length(Arguments));
    for i := Low(Arguments) to High(Arguments) do
    begin
      paramIndexes[i] := i + 1;
      params[i] := Variant(Arguments[i]);
    end;

    ReturnValue := ObjectInvoke(instance, methodInfo, paramIndexes, params);
    if not VarIsEmpty(ReturnValue) then
      VarCopy(Variant(Dest), ReturnValue);
  end
  else
  begin
    VarClear(Variant(Dest));
  end;
end;

function TDuckVariantType.GetInstance(const V: TVarData): TObject;
begin
  Result := TDuckVarData(V).VDuck;
end;

function Duck(Instance: TObject): Variant;
begin
  TDuckVarData(Result).VType := DuckVariantType.VarType;
  TDuckVarData(Result).VDuck := Instance;
end;

initialization
  DuckVariantType := TDuckVariantType.Create;

finalization
  FreeAndNil(DuckVariantType);

end.

你可以像这样简单地使用它:

You can simply use it like this:

type
  {$METHODINFO ON}
  TDuck = class
  public // works in XE, not sure if it needs to be published in older versions
    procedure Quack;
  end;

procedure TDuck.Quack;
begin
  ShowMessage('Quack');
end;

procedure DoSomething(D: Variant);
begin
  D.Quack;
end;

var
  d: TDuck;
begin
  d := TDuck.Create;
  try
    DoSomething(Duck(d));
  finally
    d.Free;
  end;
end;

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