Duck typing in Delphi 2007 (Continued)? - delphi

Question

This is a follow up to this post.
I refined my requirement based on the accepted answer posted here.
My *.dpr file:
program DuckD11;
{$APPTYPE CONSOLE}
uses
SysUtils,
uDuckTyping in 'uDuckTyping.pas',
uBirds in 'uBirds.pas';
procedure DoSomething(AObject: TObject);
begin
Duck(AObject).Quack;
end;
var
Bird: TBird;
Ganagana: TGanagana;
Canard: TCanard;
begin
Writeln('Duck typing :');
Writeln;
Bird := TBird.Create('Bird');
try
DoSomething(Bird);
finally
Bird.Free;
end;
Ganagana := TGanagana.Create;
try
DoSomething(Ganagana);
finally
Ganagana.Free;
end;
Canard := TCanard.Create;
try
DoSomething(Canard);
finally
Canard.Free;
end;
Readln;
end.
uBirds.pas listing:
unit uBirds;
interface
uses
SysUtils;
type
{$METHODINFO ON}
TBird = class
private
FName: string;
public
constructor Create(AName: string);
procedure Quack;
end;
TGanagana = class
private
const cName = 'Ganagana';
public
procedure Quack;
end;
TCanard = class
private
const cName = 'Canard';
public
procedure Quack;
end;
{$METHODINFO OFF}
implementation
{ TBird }
constructor TBird.Create(AName: string);
begin
FName := AName;
end;
procedure TBird.Quack;
begin
Writeln(Format(' %s->Quack',[Self.FName]));
end;
{ TGanagana }
procedure TGanagana.Quack;
begin
Writeln(Format(' %s=>Quack',[Self.cName]));
end;
{ TCanard }
procedure TCanard.Quack;
begin
Writeln(Format(' %s::Quack',[Self.cName]));
end;
end.
My attempt coding uDuckTyping.pas:
unit uDuckTyping;
interface
type
IDuck = interface
['{41780389-7158-49F7-AAA5-A4ED5AE2699E}']
procedure Quack;
end;
function Duck(AObject: TObject): IDuck;
implementation
uses
ObjAuto;
type
TDuckObject = class(TInterfacedObject, IDuck)
private
FObj: TObject;
// ???
protected
procedure Quack;
public
constructor Create(AObject: TObject);
end;
function Duck(AObject: TObject): IDuck;
begin
Result := TDuckObject.Create(AObject);
end;
{ TDuckObject }
constructor TDuckObject.Create(AObject: TObject);
begin
FObj := AObject;
// ???
end;
procedure TDuckObject.Quack;
begin
// ???
end;
end.
My question:
I want to use
ObjAuto.GetMethodInfo to ascertain the existence of the wrapped Quack method.
ObjAuto.ObjectInvoke to invoke the wrapped Quack method.
How can I complete the code ?

Answer 1

I end up getting it to work after many trial:
Modifications in the uDucktyping.pas unit:
Fields added as private in TDuckObject class definition
FQuackPMethodInfo: PMethodeInfoHeader;
FParamIndexes: array of Integer;
FParams: array of Variant;
Initialization of FQuackPMethodInfo in TDuckObject.Create implementation
FQuackPMethodInfo := GetMethodInfo(AObject, ShortString('Quack'));
To append just after FObj initialization statement.
Invokation of "Quack" within TDuckObject.Quack implementation
if Assigned(FQuackPMethodInfo) then
ObjectInvoke(FObj, FQuackPMethodInfo, FParamIndexes, FParams);