Hi,

I'm playing a bit with the notion of execute a method dynamically on demand. I'ved created the following PoC:
https://gist.github.com/2950789

It works, but for some strange reason, I find myself feeling that I'm missing something, or it should be done differently. Does this code written properly, or should I do it differently ?

Thanks,
Ido

2012/6/18 ik :

Souldn't this be

Exec: procedure of object;

instead of only procedure? Imho one pointer alone can not be enough, it should need the address of the procedure *and* the address of the object instance. Does your example work with multiple instances of the same class? If yes then I really don't understand why. But I also did not test it myself.

Seems to work for me, updated the example: https://gist.github.com/2950789

Or am O missing something ?

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Seems to work for me, updated the example: https://gist.github.com/2950789 Or am O missing something ?

Change your method to

procedure TMyClass.SayHi;
begin
  writeln('Hi World from '+IntToStr(ptruint(self)));
end;

And the test to

 write('From MyClass2 : ');
 MyClass2.SayHi;
 if not ExecMethod(MyClass2, 'SayHi') then
   writeln(STDERR, 'Could not find SayHi method on MyClass2 instance');

And you'll get something like:

From MyClass : Hi World from 482800

Hi World from 4199728

From MyClass2 : Hi World from 482816

Hi World from 4199728

As Bern said you can't call an object method without passing the reference to the instance. In this case you are lucky because TMyClass.SayHi doesn't use any properties or class vars. Add a property to TMyClass and try to writeln that property and you will see it fails. What you are doing here is calling SayHi as if it where a class method.

Ludo

function ExecMethod(Instance : TObject; Name : String) : Boolean;
var Exec : TMethod;
begin
  Exec.Code := TProcedure(Instance.MethodAddress(Name));
  Exec.Data := Instance;
  Result := Assigned(Exec.Code);
  if Result then TProcedureOfObject(Exec)();
end;

Mattias

Here is the correct way of doing it:

function ExecMethod(Instance : TObject; Name : String) : Boolean;
type
  TProc= procedure of object;
var
  method : TMethod;
  exec:tproc;
begin
  method.Data := Pointer(Instance);
  method.Code := Instance.MethodAddress(Name);
  Exec:=TProc(Method);
  Result := Assigned(method.Code);
  if Result then Exec;
end;

Output:

From MyClass : Hi World from 482800

Hi World from 482800

From MyClass2 : Hi World from 482816

Hi World from 482816

Ludo

Thank you Ludo, Mattias and Bernd.
It works well now :)

Ido