From: Markus Gaelli <gaelli@...>
Date: 2006-09-01T08:16:24+09:00
Subject: Fwd: [Q] How would you do method extensions (sometimes called class extensions) in Ruby?

Begin forwarded message:

> From: Markus Gaelli <gaelli@emergent.de>
> Date: August 31, 2006 11:07:26 PM GMT+02:00
> To: ruby-core@ruby-lang.org
> Subject: [Q] How would you do method extensions (sometimes called  
> class extensions) in Ruby?
>
> Hi List,
>
> (1) The Problem: Bridge Gap between Tests and Documentation with  
> Executable Examples
> May I introduce myself shortly: I am a long-term OOer using mainly  
> Smalltalk until now [0] - and I am interested in bridging the gap  
> between documentation (static, bound (comments possible for classes  
> and methods), often outdated) and unit testing (dynamic, unbound  
> [2], up to date) by the metaphor of examples.
>
> (2) The Concept
> I'd like to be able to see exemplified calls for methods ("method  
> examples") - and compose new method examples using example  
> instances of classes - which in turn are created by "method  
> examples" [3]
>
> (3) The Proof of Concept
> I have some prototypes for "Eg" in Smalltalk [3], but wonder how it  
> would be possible to do something like this in Ruby.
>
> (4) My Approach in Smalltalk: Relying on Conventions and Method  
> Extensions
>
> (4.1) Exemplifying Classes
> The easiest solution to bind examples at least to their classes  
> (where they should give an exemplified instance of) is by making  
> them factory methods of them on the class side. At least in  
> Smalltalk you can see this pattern a lot (usually these class  
> methods also start with "example..."), I am sure Ruby folks do  
> something similar.
>
> (4.2) Exemplifying and Testing Methods
> I just say that the last method called in these class methods is  
> the one exemplified by this example. So this is how I can bind the  
> methods to their "method examples" in a light-way and very readable  
> manner.
>
> If the method under test (yes, the last one called in the factory  
> method / example method) has some postconditions I would declare  
> this method to be a "checked method example".
> If there are some assertions in the "method example" itself, I take  
> the last method called before the assertions as the tested/ 
> exemplified method. I  call these kind of "commands" "method tests".
> Note that these "method commands" do return an instance of the  
> class they are bound to. This is my invariant for storing them and  
> also ensures that the instances they create can be reused by higher- 
> level examples/ tests. I do not believe tests should be "void" as  
> JUnit, one only needed to call the highest level tests, which in  
> turn can call lower level ones. And yes - all tests shall be side  
> effect free, and everything but the return value should get garbage  
> collected after a test is over.
>
> (5) Finally: My Concrete Problem
> As you can see I am heavily relying on conventions to keep the code  
> readable, but still machine parsable. But for doing so I need to  
> denote these "method commands" (including "method examples",  
> "checked method examples" and "method tests") as being of this  
> kind. Besides many people do not like the idea to deploy their code  
> together with tests, so they needed to be separable.
>
> This is fine in Smalltalk, as we have method extensions, which  
> scope allow Smalltalkers to add methods to classes in packages, in  
> which these classes have _not_ been originally defined, but how  
> would you do this in Ruby?
>
> I am aware of Singleton Methods, but as they can extend instances,  
> (how) can I extend classes without changing their original class  
> definition in Ruby?
>
> I would be very grateful for some help, or pointers - certainly I  
> wouldn't mind if somebody stole this idea, actually I'd love to see  
> "Eg" ported to Ruby, but I am lacking a bit time to do it myself: I  
> have to finish my PhD soon and then a Smalltalk (Seaside) job to  
> start.
> - But I do would like not to look too Smalltalk-Snobbish and  
> include some help in my PhD to any guys of other fine languages,  
> who decided some day, that this might be a good idea.
>
> Cheers,
>
> Markus
>
> [1] http://www.iam.unibe.ch/~scg/cgi-bin/scgbib.cgi?query=gaelli
> [2] Markus Gaelli, Michele Lanza and Oscar Nierstrasz, �Towards a  
> Taxonomy of SUnit Tests,� Proceedings of ESUG 2005 (13th  
> International Smalltalk Conference), September 2005.
> http://www.iam.unibe.ch/~scg/Archive/Papers/ 
> Gael05aTowardsATaxonomyOfUnitTests.pdf
> [3] Markus Gaelli, Oscar Nierstrasz and St�phane Ducasse, �One- 
> Method Commands: Linking Methods and Their Tests,� OOPSLA Workshop  
> on Revival of Dynamic Languages, October 2004.
> http://www.iam.unibe.ch/~scg/Archive/Papers/ 
> Gael04cLinkingMethodsAndTests.pdf