Re: [dws-developer] Destructor

[Andreas L. <alu...@we...>]

Mark wrote:

>> Third I think that assertion questions like
>>
>>   Assert((ExternalObject<>nil) and (ExternalObject is TStringList));
>>
>> can be optimized to
>>
>>   Assert(ExternalObject is TStringList);
>>
>> Am I right?
>>
>> OK, time to go to bed ..., ALu.
> 
> 
> No. I had to double check to make sure. Here is some Delphi code to try 
> out.
> 
> var
>   sl: TStringList;
>   someObject: TObject;
> begin
>   sl := nil;
>   someObject := sl;
> 
>   if someObject is TStringList then
>     showMessage('I''m a TStringList');
> end;
> 
> Using D5, the message does not show.
> 

"sl is TStringList" also results to "False". First check of the
"is"-operator is the test "pointer=nil?" (see CPU Window). So I think
there is no need for the nil check.

> Hmm. I think this would work better: (haven't tried it... could be wrong)
>
> Info.Result := Info.RegisterExternalObject(TMyStringList.Create, True,
> False);
>

Yes, this may work. But I (as user) would NEVER understand, why NO 
constructor is called, when creating a new object. That's why I am not a 
fan of "your" RegisterExternalObject function (Sorry). A similar 
question is unanswered in the forum (2003/12/21 "Why doesn't the 
constructor get called?"). I do not have a convincing answer ... :(

> This was intentional. I thought that declaring the destructor was wasted 
> memory (extra symbols) because all you need to do is call .Free and 
> TObject implements that. Was I wrong to do this? Does *every* class need 
> a destructor or is an ancestor declared one okay?

I like the idea to reintroduce the Free-Method (copy-paste of Delphi 
code ;) ).
If no one of the developers raises an objection ... I can start a try
(hello Matthias?). But for your problem: Sometimes I take quasi-fix 
objects as ExternalObjects (the current form, a button, ttable, tgrid, 
etc.) Such an object must not freed at destruction of the IScriptObj. So 
a general destruction of the ExternalObject in "TObject.Destroy" (DWS) I 
will not support. I would introduce a new flag in TScriptObj?!

Regards, ALu.