# Include module and class inheritance? which one to choose? **URL:** \ **Category:** Ruby\ **Created:** [April 9, 2008, 5:51am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233 "2008-04-09T05:51:10Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 5:51am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/1 "2008-04-09T05:51:10Z")
What is the different between the including a module and inherit a class? For me, there seems to be almost the same. The only thing is module can be think as an abstract class which is not instantiate able. If you include a module, you get all the methods from the module. You can override the function and call super to call the method from the module. This look the same as the class inherit. So, I am confusing on which one should I use? Create a module, include it or create a class and inherit it? Thanks. ---
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 6:47am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/2 "2008-04-09T06:47:25Z")
A module is simply a place where you can store methods. Thus, you can include a module as a mixin in a class, and it will get all the methods. Julian. Learn Ruby on Rails! Check out the FREE VIDS (for a limited time) VIDEO #3 out NOW! [http://sensei.zenunit.com/](http://sensei.zenunit.com/) ---
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 7:32am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/3 "2008-04-09T07:32:24Z")
Julian L. wrote: > A module is simply a place where you can store methods. > > Thus, you can include a module as a mixin in a class, and it will get > all the methods. Yes, but we can achieve the same thing by inherit a class which will get all the methods also.I know we can mixin multiple classes but only inherit 1 class. If there is only 1 class/module, which we should use? create a module or class? ---
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 7:40am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/4 "2008-04-09T07:40:01Z")
It depends what you want to do - do you need to use the superclass separately? Julian Learn Ruby on Rails! Check out the FREE VIDS (for a limited time) VIDEO #3 out NOW! [http://sensei.zenunit.com/](http://sensei.zenunit.com/) ---
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 8:25am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/5 "2008-04-09T08:25:44Z")
On 09.04.2008 07:32, Shin guey Wong wrote: > class? > If you need to instantiate it make it a class. Everything that could be > viewed as an “item” should probably be a class (where “item” could as > well be a complex algorithm, see “command pattern”). A module on the > other hand is more like a container for functionality that can be used > in multiple places. It can be either completely independent or - more > common I believe - rely on some other methods for interfacing (like > Enumerable relies on #each being defined). Just look at modules defined > in the standard library to get an idea how they are used (for example > Comparable, Enumerable). Kind regards robert ---
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 7:58am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/6 "2008-04-09T07:58:12Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Shin guey Wong wrote: | Julian L. wrote: |\> A module is simply a place where you can store methods. |\> |\> Thus, you can include a module as a mixin in a class, and it will get |\> all the methods. |\> | | Yes, but we can achieve the same thing by inherit a class which will get | all the methods also.I know we can mixin multiple classes but only | inherit 1 class. | If there is only 1 class/module, which we should use? create a module or | class? Yes. 😛 It depends, actually. A module provides a namespace, and (ideally) prevents namespace collisions. It also provides grouping of classes (well, d’uh. I’m amazed at my insightfulness at this early hour…). Let’s say you have an application, which brings its own String, Math, and Array functions. If you put them into the Module MyApplication, you prevent collisions with Ruby’s String, Math, and Array functions. Additionally, you can mixin these methods, while maintaining the ability to inherit from the classes you have in your modules, if need be. (You can inherit from Digest::MD5, for example.) Also, only a module can include a module. In short: It depends on your scenario. * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Make the coupling between modules visible. ~ - The Elements of Programming Style (Kernighan & Plaugher) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkf8WtgACgkQbtAgaoJTgL8CZACgk0bY83eL9DX8JZExeXfBJfs+ xpkAnibP1+clUdU5ii7Dzv1UAvZPLzL6 =5zTq -----END PGP SIGNATURE----- ---
**Author:** ![shinwoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/df705f/32.png) [@shinwoo](https://www.ruby-forum.com/u/shinwoo)\ **Post date:** [April 9, 2008, 10:30am UTC](https://www.ruby-forum.com/t/include-module-and-class-inheritance-which-one-to-choose/134233/7 "2008-04-09T10:30:51Z")
On Apr 9, 7:32 am, Shin guey Wong [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Yes, but we can achieve the same thing by inherit a class which will get > all the methods also.I know we can mixin multiple classes but only > inherit 1 class. > If there is only 1 class/module, which we should use? create a module or > class? You need to approach this issue in terms of semantics rather than behaviour. It’s true that inheriting from a class and including a module are very similar in behaviour. However, in terms of semantics classes and modules are miles apart: - Look at the Ruby standard library. Module names are usually adjectives (often ending in -able) while classes are usually nouns. The meaning is that modules are meant to be containers of functionality which is not dependent on a specific object, but is potentially useful for many (Comparable, for instance, is useful not only for numbers, but also for strings, which are unrelated classes). Classes, on the other hand, are used to instantiate items which can be manipulated further. To give a real world-like example, classes are blueprints from which machines can be built. Modules are more like expansion packs, which can be plugged in existing machines to extend their behaviour. - Even when Modules are named with nouns, the semantics remain. For instance, the Math module is clearly a container of functionality (maths functions, in this case). A Math object wouldn’t make much sense (you can’t manipulate maths, it’s just a given set of laws you can choose to use). - Don’t forget that inheritance also has a strong semantic meaning: it represents strictly an “is-a” relationship between objects. Use it only if both your classes should be instantiatable, and if the subclass could, for all intents and purposes, replace the superclass in every case the superclass could be used (a subclass should only refine behaviour, and only redefine it if it doesn’t jeopardise this “is-a” relationship). Including a module, on the other hand, has a looser semantic meaning: it represents a “has-a” relationship, indicating that the object including the module gains the functionality contained by the module, and that it makes sense for it to have it. I know it looks like a lot to consider in a 1 module/class case. However, I’d still advise you to give it full attention and decide on using a module or a class based on semantics rather than just behaviour. First, you never know whether what you’re doing right now won’t need to be extended later, and it will be easier if the semantics make sense. Second, by thinking this through in a simple case, you train yourself to think semantically in more complicated cases, where you have more chunks of functionality to account for and more complicated configurations to disentangle. So stop looking just at adding methods to a class. Take a step back and consider what those methods together _define_. Do they define something that could be considered an object, a machine or item that could be meaningfully manipulated? Then make it a class, and subclass from it (if you can maintain the “is-a” relationship). If those methods define just a chunk of functionality, rather than describe an object, put them in a module, and include it in a class.