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.blogspot.com
Portfolio: http://www.gilesgoatboy.org
Tumblelog: http://giles.tumblr.com/
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
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 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
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
On 17.10.2007 21:22, Giles Bowkett wrote:
from :0
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.
]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
endBut you don't need to think this way in Ruby -- unlike Java, Ruby is
weakly typed.-- Thomas Adam
--
-yossef
Hi --
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
endBut 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
endUgly, isn't it? Of course, that's just more fuel for the "don't do
this in Ruby" fire.
You could do:
class C
private_class_method :new
def self.inherited(c)
class << c; public :new; end
end
end
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.
David
On Thu, 18 Oct 2007, Yossef Mendelssohn wrote:
]On Oct 17, 2:41 pm, "Thomas Adam" <thomas.ada...@gmail.com> wrote:
On 17/10/2007, Giles Bowkett <gil...@gmail.com> wrote:
--
Upcoming training from Ruby Power and Light, LLC:
* Intro to Ruby on Rails, Edison, NJ, October 23-26
* Advancing with Rails, Edison, NJ, November 6-9
Both taught by David A. Black.
See http://www.rubypal.com for more info!
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.
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.
--
Rick DeNatale
My blog on Ruby
http://talklikeaduck.denhaven2.com/
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.blogspot.com
Portfolio: http://www.gilesgoatboy.org
Tumblelog: http://giles.tumblr.com/
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
On 10/18/07, Giles Bowkett <gilesb@gmail.com> wrote:
--
what do I think about Ruby?
http://ruby-smalltalk.blogspot.com/