[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.ruby

abstract superclasses

Giles Bowkett

10/17/2007 7:23:00 PM

I sometimes use the Java thing of an abstract superclass in Ruby. I
usually just set up the abstract parent so that it'll break if used
directly. Is it better to just use Modules? Have other people run into
this?

--
Giles Bowkett

Blog: http://gilesbowkett.bl...
Portfolio: http://www.gilesg...
Tumblelog: http://giles.t...
7 Answers

Robert Klemme

10/17/2007 7:40:00 PM

0

On 17.10.2007 21:22, Giles Bowkett wrote:
> I sometimes use the Java thing of an abstract superclass in Ruby. I
> usually just set up the abstract parent so that it'll break if used
> directly. Is it better to just use Modules? Have other people run into
> this?

Why bother? If your "abstract" class requires a method to be present
then just not defining it works pretty well - in modules as well as in
classes:

irb(main):001:0> o=Object.new.extend Enumerable
=> #<Object:0x1001a92c>
irb(main):002:0> o.map {|y| y.to_i}
NoMethodError: undefined method `each' for #<Object:0x1001a92c>
from (irb):3:in `map'
from (irb):3
from :0
irb(main):003:0>

Of course you need some documentation about the missing method - that
would probably be the only reason why I'd add a dysfunctional definition
of that method...

Kind regards

robert

Thomas Adam

10/17/2007 7:41:00 PM

0

On 17/10/2007, Giles Bowkett <gilesb@gmail.com> wrote:
> I sometimes use the Java thing of an abstract superclass in Ruby. I
> usually just set up the abstract parent so that it'll break if used
> directly. Is it better to just use Modules? Have other people run into
> this?

I'd use a Module, yes. Or a class:

class SomeClassMimickingAbstract
private_class_method :new
end

But you don't need to think this way in Ruby -- unlike Java, Ruby is
weakly typed.

-- Thomas Adam

Yossef Mendelssohn

10/18/2007 12:18:00 AM

0

]On Oct 17, 2:41 pm, "Thomas Adam" <thomas.ada...@gmail.com> wrote:
> On 17/10/2007, Giles Bowkett <gil...@gmail.com> wrote:
>
> > I sometimes use the Java thing of an abstract superclass in Ruby. I
> > usually just set up the abstract parent so that it'll break if used
> > directly. Is it better to just use Modules? Have other people run into
> > this?
>
> I'd use a Module, yes. Or a class:
>
> class SomeClassMimickingAbstract
> private_class_method :new
> end
>
> But you don't need to think this way in Ruby -- unlike Java, Ruby is
> weakly typed.
>
> -- Thomas Adam

How do you suggest to use that class? I understanding keeping the
"abstract" class from being instantiated, but what about the concrete
classes, the ones you're going to use?

class RealThing < SomeClassMimickingAbstract
# now make .new public again
end

Ugly, isn't it? Of course, that's just more fuel for the "don't do
this in Ruby" fire.

--
-yossef

David A. Black

10/18/2007 1:40:00 AM

0

Rick DeNatale

10/18/2007 2:29:00 AM

0

On 10/17/07, David A. Black <dblack@rubypal.com> wrote:

>
> I've actually never felt the need for abstract classes in Ruby
> programs. I'm not a Java programmer, so it never would have occurred
> to me in that context, and I haven't found myself inventing it for
> Ruby.

Note that ActiveRecord has a slightly different spin on the notion of
abstract class.

ActiveRecord::Base has a rw attribute called abstract_class and an
abstract_class? predicate method.

ActiveRecord::Base subclasses can be 'set' as abstract the meaning is
that such classes don't have a corresponding database table. They are
used as intermediate superclasses, typically to let a set of AR
classes to inherit a common database connection different from other
AR classes in the same application.


--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denh...

Giles Bowkett

10/18/2007 3:31:00 AM

0

It is a Java thing; it comes from "Refactoring," I think, the Martin
Fowler book. The idea is you handle excessive if/else/etc. statements
by creating classes and putting the different code branches in
subclasses. Since you'll have pieces which don't need to be different
in the subclasses, you keep those pieces in the superclass so you have
them in one place.

In practice I usually do the unimplemented method thing, so that
misusing the code just makes things blow up. The method hiding and
revealing is probably overkill, although if you extract it into a
module, you can have an AbstractSuperclass module pretty easily, which
is a gajillion times better than comments which say "abstract
superclass!! do not instantiate!!!".

As a refactoring it's generally pretty useful. The code becomes easier
to test and easier to read. But it's really not idiomatic at all, and
it's very inelegant.

--
Giles Bowkett

Blog: http://gilesbowkett.bl...
Portfolio: http://www.gilesg...
Tumblelog: http://giles.t...

Robert Dober

10/18/2007 8:52:00 AM

0

On 10/18/07, Giles Bowkett <gilesb@gmail.com> wrote:
I'd go for modules but Robert is right too, if a class just is
abstract by the way it is defined or refactored that's it, no way
checking it's instantiation, no please. If you really feel that an
entity shall not be instantiated than a Module seems to be the correct
Ruby device.

Cheers
Robert

--
what do I think about Ruby?
http://ruby-smalltalk.blo...