[Seaside] Dynamic typing in smalltalk

[Sebastian Heidbrink]

As far as I can see there's no need for your loop.
John's solution already provides you with a class in selectedType.

Eventhough it isn't quite the way to do it.
You forgot something here. Symbol new returns a Symbol:

  dynamicTyping := ('PaperBibli', selectedType) asSymbol asClass.
bibEntry := PaperBibli perform: dynamicTyping new.

asClass isn't nice because it take some while and there are more 
OO-solutions available.
Try to get away from casting. Delegation is the answer.

If you might need to keep your original Object, or, how to say this 
right now, whish or need to keep on using the memory space you could 
also use become: or becomeWith:
Now this is really not the nice way to do it, but it schould also work.

yourmessage: aPaperBibli
^PaperArticle new become: aPaperBibli

Just to be mentioned...

I would use John's approch, it's the most common.

Sebastian

Am 29.10.2010 20:23, schrieb Alexandre BP:
> thanks for your time,
> Your second solution seems very nice I'll try it as soon as possible.
>
> The second one however forces me to have a big list of loops that look 
> like '(selectedType = 'Book') ifTrue: [var := PaperBibliArticle new]. '
> which is neither clean nor evolutive.
> I wanted to do something like:
>
>  dynamicTyping := ('PaperBibli', selectedType, ' new') asSymbol.
> bibEntry := PaperBibli perform: dynamicTyping.
>
> OR
>
>  dynamicTyping := ('PaperBibli', selectedType) asSymbol.
> bibEntry := PaperBibli perform: dynamicTyping new.
>
> --> it doesn't work unfortunately ...
>
> OR:
>
> As in JAVA:
>
> PaperBibli bibEntry;
>
> (when I need it)
> bibEntry = new PaperBibliArticle;
>
> Anyway I'll try the second solution which is more elegant.
> thank you very much
> alex
>
>
>
> > Date: Fri, 29 Oct 2010 13:56:14 -0300
> > From: andres at lifia.info.unlp.edu.ar
> > To: seaside at lists.squeakfoundation.org
> > Subject: Re: [Seaside] Dynamic typing in smalltalk
> >
> > Hi Alexandre,
> > I guess you could try two approaches:
> >
> > 1. Just list the classes in a select, so that the first step is 
> choosing
> > the entry. Once you have this you just create the appropriate class.
> >
> > 2. Decouple the type of the object from the object itself (check also
> > http://www.ksc.com/article3.htm). Thus PaperBibli would know an object
> > (lets say PaperType) whose subclasses would be Book, Article, etc. When
> > the user selects the type he wants you just set the object's type. The
> > type class is the one that holds the type-specific information.
> >
> > HTH,
> > Andrés
> >
> > Alexandre BP escribió:
> > > thank you for your replyI have a class named "PaperBibli" which 
> keeps a list of bibliographic entries.Those entries are of different 
> type: Article, Book, Conference,...Every type has its own fields such 
> as: author,title,...
> > > --> I created SubClasses of "PaperBibli" for each type so that 
> when I instanciate an bibliographic entry I don't have lots of 
> variables(fields) which are empty because not required in a particular 
> type.The problem is that when I instanciate my bibliographic entry I 
> still don't know of which type it is because the user tell me so by 
> choosing in a scroll list.
> > > I hope that my explanation is clear
> > >
> > >
> > >
> > > Date: Fri, 29 Oct 2010 12:24:22 -0400
> > > Subject: Re: [Seaside] Dynamic typing in smalltalk
> > > From: sean at monkeysnatchbanana.com
> > > To: seaside at lists.squeakfoundation.org
> > >
> > > There are types in smalltalk. Each object has a type.
> > > That aside, what are you trying to accomplish with your example below?
> > >
> > > On Fri, Oct 29, 2010 at 12:13 PM, Alexandre BP 
> <abalonpe at ulb.ac.be> wrote:
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Hello,
> > > I would like to know if it is possible to apply dynamic typing in 
> smalltalk. For example, If I want to use polymorphism, it would be:
> > > var := Class new. var := (SubClass1) message. var := (SubClass2) 
> message.
> > >
> > > Where message from SubClass1 is different then the one from 
> SubClass2.Is there any solution for my problem? I know that there is 
> no type in smalltalk but there is definitely a way to use polymorphism 
> right?
> > >
> > > Thank you in advance,Regardsalex
> > >
> > > _______________________________________________
> > >
> > > seaside mailing list
> > >
> > > seaside at lists.squeakfoundation.org
> > >
> > > http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/seaside
> > >
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > seaside mailing list
> > > seaside at lists.squeakfoundation.org
> > > http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/seaside
> > >
> > >
> > > 
> ------------------------------------------------------------------------
> > >
> > > _______________________________________________
> > > seaside mailing list
> > > seaside at lists.squeakfoundation.org
> > > http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/seaside
> > _______________________________________________
> > seaside mailing list
> > seaside at lists.squeakfoundation.org
> > http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/seaside
>
>
> _______________________________________________
> seaside mailing list
> seaside at lists.squeakfoundation.org
> http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/seaside

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.squeakfoundation.org/pipermail/seaside/attachments/20101029/1eb78b3f/attachment.htm