Re: [Pharo-users] casting to subclass

[Siemen Baader]

On Fri, Mar 2, 2018 at 9:19 PM, Hernán Morales Durand <
hernan.mora...@gmail.com> wrote:

> Hi Siemen
>
> IIRC this was known as "wide classes", there is some paper about it.
>

Thanks for the pointer! I found
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.31.4708 but no
Pharo implementation. Was it available in Pharo at some point?

cheers
Siemen


Cheers,
>
> Hernán
>
> 2018-03-02 15:45 GMT-03:00 Siemen Baader :
> > Hi all,
> >
> > it seems like we cannot cast the class of object to its subclass if that
> > subclass has had new instance variables added to it:
> >
> > http://forum.world.st/changing-the-class-of-an-existing-
> object-to-a-subclass-td4239041.html
> >
> > But I (think) I need it - I'm transforming a DOM tree from
> XMLHTMLParser's
> > XMLElement s to a subclass of Iliad's ILHTMLBuilderElement s, and for
> single
> > occurences I would like to use the more specific subclasses, like
> > ILCheckboxElement. I can make the cast manually, I know when it is safe
> to
> > do.
> >
> > What else could I do, apart from removing the element from its tree,
> > creating a new (subclass) instance and then putting this element in
> place of
> > the old one? Some #perform or `super` magic..?
> >
> > hm..
> >
> > thanks for any pointers!
> >
> > -- Siemen
>
>

Re: [Pharo-users] casting to subclass

[Siemen Baader]

On Fri, Mar 2, 2018 at 9:21 PM, Esteban A. Maringolo 
wrote:

> "Castings" are aliens in the Smalltalk world, although there is a
> #become*: method family, I would discourage you from using it as an
> alternative unless you really need to do it.
>

Ok, thanks. I think this use case is specific enough for casting to be
useful, but I see your point.

>
> If your use case is that concrete, I'd do something like:
>
> `ILHTMLBuilderElement fromXMLElement: anXMLElement`
>

Yes.. :)

-- Siemen


>
> Then all subclasses of `ILHTMLBuilderElement` will know what to look
> and what to omit from the `XMLElement` parameter.
>
> Regards!
>
> Esteban A. Maringolo
>
>
> 2018-03-02 17:08 GMT-03:00 Stephan Eggermont :
> > Siemen Baader  wrote:
> >>
> >> What else could I do, apart from removing the element from its tree,
> >> creating a new (subclass) instance and then putting this element in
> place
> >> of the old one? Some #perform or `super` magic..?
> >
> > Use composition? Generate accessing code where necessary.
> > Is this very performance critical code?
> >
> > Stephan
> >
> >
> >
>
>

Re: [Pharo-users] casting to subclass

[Siemen Baader]

On Fri, Mar 2, 2018 at 9:08 PM, Stephan Eggermont  wrote:

> Siemen Baader  wrote:
> >
> > What else could I do, apart from removing the element from its tree,
> > creating a new (subclass) instance and then putting this element in place
> > of the old one? Some #perform or `super` magic..?
>
>
Use composition? Generate accessing code where necessary.
>

Hm yes.. This is probably what I'll end up doing eventually. I was trying
to save a lot of typing work. XMLElement and ILHTMLBuilder both have useful
interfaces, and some of it is called from behind the scenes by their
respective frameworks.

> Is this very performance critical code?

I don't think so. But it is the HTML construction code of a web app, so it
*might* become a bottleneck. I don't treat it like this ATM.

Siemen

>
> Stephan
>
>
>
>

Re: [Pharo-users] casting to subclass

[Esteban A. Maringolo]

"Castings" are aliens in the Smalltalk world, although there is a
#become*: method family, I would discourage you from using it as an
alternative unless you really need to do it.

If your use case is that concrete, I'd do something like:

`ILHTMLBuilderElement fromXMLElement: anXMLElement`

Then all subclasses of `ILHTMLBuilderElement` will know what to look
and what to omit from the `XMLElement` parameter.

Regards!

Esteban A. Maringolo


2018-03-02 17:08 GMT-03:00 Stephan Eggermont :
> Siemen Baader  wrote:
>>
>> What else could I do, apart from removing the element from its tree,
>> creating a new (subclass) instance and then putting this element in place
>> of the old one? Some #perform or `super` magic..?
>
> Use composition? Generate accessing code where necessary.
> Is this very performance critical code?
>
> Stephan
>
>
>

Re: [Pharo-users] casting to subclass

[Hernán Morales Durand]

Hi Siemen

IIRC this was known as "wide classes", there is some paper about it.
Cheers,

Hernán

2018-03-02 15:45 GMT-03:00 Siemen Baader :
> Hi all,
>
> it seems like we cannot cast the class of object to its subclass if that
> subclass has had new instance variables added to it:
>
> http://forum.world.st/changing-the-class-of-an-existing-object-to-a-subclass-td4239041.html
>
> But I (think) I need it - I'm transforming a DOM tree from XMLHTMLParser's
> XMLElement s to a subclass of Iliad's ILHTMLBuilderElement s, and for single
> occurences I would like to use the more specific subclasses, like
> ILCheckboxElement. I can make the cast manually, I know when it is safe to
> do.
>
> What else could I do, apart from removing the element from its tree,
> creating a new (subclass) instance and then putting this element in place of
> the old one? Some #perform or `super` magic..?
>
> hm..
>
> thanks for any pointers!
>
> -- Siemen

Re: [Pharo-users] casting to subclass

[Stephan Eggermont]

Siemen Baader  wrote:
> 
> What else could I do, apart from removing the element from its tree,
> creating a new (subclass) instance and then putting this element in place
> of the old one? Some #perform or `super` magic..?

Use composition? Generate accessing code where necessary. 
Is this very performance critical code?

Stephan

[Pharo-users] casting to subclass

[Siemen Baader]

Hi all,

it seems like we cannot cast the class of object to its subclass if that
subclass has had new instance variables added to it:

http://forum.world.st/changing-the-class-of-an-existing-object-to-a-subclass-td4239041.html

But I (think) I need it - I'm transforming a DOM tree from XMLHTMLParser's
XMLElement s to a subclass of Iliad's ILHTMLBuilderElement s, and for
single occurences I would like to use the more specific subclasses, like
ILCheckboxElement. I can make the cast manually, I know when it is safe to
do.

What else could I do, apart from removing the element from its tree,
creating a new (subclass) instance and then putting this element in place
of the old one? Some #perform or `super` magic..?

hm..

thanks for any pointers!

-- Siemen