# Abstract superclasses **URL:** \ **Category:** Ruby\ **Created:** [October 17, 2007, 9:23pm UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535 "2007-10-17T21:23:41Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 17, 2007, 9:23pm UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/1 "2007-10-17T21:23:41Z")
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 B. Blog: [http://gilesbowkett.blogspot.com](http://gilesbowkett.blogspot.com) Portfolio: [http://www.gilesgoatboy.org](http://www.gilesgoatboy.org) Tumblelog: [http://giles.tumblr.com/](http://giles.tumblr.com/) ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 17, 2007, 9:42pm UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/2 "2007-10-17T21:42:26Z")
On 17/10/2007, Giles B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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 A. ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 17, 2007, 9:45pm UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/3 "2007-10-17T21:45:57Z")
On 17.10.2007 21:22, Giles B. 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 # 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 ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 18, 2007, 2:19am UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/4 "2007-10-18T02:19:06Z")
]On Oct 17, 2:41 pm, “Thomas A.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ``` > private_class_method :new > > ``` > > end > > But you don’t need to think this way in Ruby – unlike Java, Ruby is > weakly typed. > > – Thomas A. 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. ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 18, 2007, 3:40am UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/5 "2007-10-18T03:40:21Z")
Hi – On Thu, 18 Oct 2007, Yossef M. wrote: > > class SomeClassMimickingAbstract > > 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. You could do: class C private\_class\_method :new def self.inherited© 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 ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 18, 2007, 5:31am UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/6 "2007-10-18T05:31:58Z")
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 B. Blog: [http://gilesbowkett.blogspot.com](http://gilesbowkett.blogspot.com) Portfolio: [http://www.gilesgoatboy.org](http://www.gilesgoatboy.org) Tumblelog: [http://giles.tumblr.com/](http://giles.tumblr.com/) ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 18, 2007, 4:30am UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/7 "2007-10-18T04:30:01Z")
On 10/17/07, David A. Black [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 18, 2007, 10:52am UTC](https://www.ruby-forum.com/t/abstract-superclasses/117535/8 "2007-10-18T10:52:51Z")
On 10/18/07, Giles B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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