# Ruby and Contract Programming (was Ruby vs. Ada) **URL:** \ **Category:** Ruby\ **Created:** [April 22, 2008, 1:59pm UTC](https://www.ruby-forum.com/t/ruby-and-contract-programming-was-ruby-vs-ada/135467 "2008-04-22T13:59:44Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [April 22, 2008, 1:59pm UTC](https://www.ruby-forum.com/t/ruby-and-contract-programming-was-ruby-vs-ada/135467/1 "2008-04-22T13:59:44Z")
Hi list I have had some thoughts about Contract Programming and Ruby, this after the recent suggestion that Ruby might have to evolve into this direction. I am a complete ignorant of CP (also aka Programming by Contract and a different copyrighted term) and that is why I was very defensive on the subject. Not having got any reply I will try to come up with some conclusions based on the little I know, hopefully nobody will take offense and rather take the opportunity to correct me where necessary. My first assumption is that Ruby and other dynamic languages do not shine on large scale projects if ( and mostly only if ) there can be no automated testing, and thus BDD/TDD cannot be applied. Whenever BDD (e.g) is applied I have much difficulties to see how CP could come into the picture. As a matter of fact one can see all the contracts in the testcases, only that we are talking behavior, which is mighty efficient. There are other quite striking parallels between CP and BDD, e.g. never write code unless it makes a failing test pass vs. define the contracts first. The remaining question would be could (and should) Ruby try to occupy other niches (talking in terms of evolution?). For the sake of argument let us say yes, I am however not at all convinced that it really should, than I guess this shall be done without sacrificing any of its dynamic qualities. So the type of contract one could establish would be to check for frozen modules/classes, or frozen traits, which I would prefer of course ;). A simple example of how a contract could look like def my\_method arg my\_module.instance\_methods.all?{ |m| arg.respond\_to? m} … I do not see what could be done more (maybe just checking the arity of the methods?) but all more sophisticated enforcements as the interface of a method just do not bear any meaning in Ruby. My conclusion would be not to go for the throat of strongly typed languages (especially not Ada or OCaml) because it would be an error to try to occupy all niches of the ecosystem in general. In particular I see CP quite inadequate for the evolution of Ruby. Ok I am duck (type-) ing now. Cheers Robert – [http://ruby-smalltalk.blogspot.com/](http://ruby-smalltalk.blogspot.com/) * * * Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein ---
**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [April 22, 2008, 2:37pm UTC](https://www.ruby-forum.com/t/ruby-and-contract-programming-was-ruby-vs-ada/135467/2 "2008-04-22T14:37:38Z")
> My conclusion would be not to go for the throat of strongly typed > languages (especially not Ada or OCaml) because it would be an error > to try to occupy all niches of the ecosystem in general. In particular > I see CP quite inadequate for the evolution of Ruby. So don’t use it then. Making it possible for others to incorporate contracts in the source wouldn’t oblige you to do so. IMHO ada and ocaml are two rather different languages. The first statically typed language that comes to mind when saying DBC would IMHO rather be Eiffel. Anyway, there is always a chance that an evolution comes to a quick halt due to inadaptability. ---
**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [April 22, 2008, 5:11pm UTC](https://www.ruby-forum.com/t/ruby-and-contract-programming-was-ruby-vs-ada/135467/3 "2008-04-22T17:11:56Z")
On Tue, Apr 22, 2008 at 2:35 PM, ThoML [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > My conclusion would be not to go for the throat of strongly typed > > languages (especially not Ada or OCaml) because it would be an error > > to try to occupy all niches of the ecosystem in general. In particular > > I see CP quite inadequate for the evolution of Ruby. > > So don’t use it then. > Making it possible for others to incorporate > contracts in the source wouldn’t oblige you to do so. Do you mean by this that CP could be done reasonably in Ruby now? I believe that it cannot be done in Ruby nowadays, that the contracts would be too weak and I believe “evolving” Ruby into that direction would not be to Ruby’s benefits. You cannot just add features without paying a price now maybe this _is_ the thing to do creating a multi paradigm language, I somehow doubt it… > IMHO ada and ocaml are two rather different languages. > Very different, indeed. > The first > statically typed language that comes to mind when saying DBC would > IMHO rather be Eiffel. > True, a good example. > > Anyway, there is always a chance that an evolution comes to a quick > halt due to inadaptability. > And not much one can do about it because it is rather difficult if not > impossible to anticipate the changes in the environment. ## Robert [http://ruby-smalltalk.blogspot.com/](http://ruby-smalltalk.blogspot.com/) * * * Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein ---
**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [April 22, 2008, 9:36pm UTC](https://www.ruby-forum.com/t/ruby-and-contract-programming-was-ruby-vs-ada/135467/4 "2008-04-22T21:36:26Z")
On Tue, Apr 22, 2008 at 9:10 PM, ThoML [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > support for metaprogramming that is currently missing (like the > Quiz #2: Implement a library that breaks the solutions from #1. > > If there is still a solution left, the answer to your question would > be yes. Yes that sounds very interesting indeed. Thx R. – [http://ruby-smalltalk.blogspot.com/](http://ruby-smalltalk.blogspot.com/) * * * Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein ---
**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [April 22, 2008, 9:11pm UTC](https://www.ruby-forum.com/t/ruby-and-contract-programming-was-ruby-vs-ada/135467/5 "2008-04-22T21:11:45Z")
> Do you mean by this that CP could be done reasonably in Ruby now? It depends what you mean with “reasonable”. I have my doubts that such a solution would cooperate well with all sorts of other meta- programming libraries. > You cannot just add features without paying a price Maybe it’s a specialization of a more general feature or maybe better support for metaprogramming that is currently missing (like the ability to rewrite code blocks/lambdas, intercepting certain method calls, making system hooks more general/robust so that several libraries can use method\_added without interfering with one another etc.). Maybe this will one day become a ruby quiz: Quiz #1: Implement class invariants in a robust/unbreakable way. Implement method advises etc. Quiz #2: Implement a library that breaks the solutions from #1. If there is still a solution left, the answer to your question would be yes.