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Re: [vox] Ruby gives you sharp knives (fwd)
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Re: [vox] Ruby gives you sharp knives (fwd)

On Wed, Apr 07, 2010 at 04:13:06PM -0700, Bill Kendrick wrote:
> A discussion about languages over on the libSDL mailing list led to this
> fellow posting a little bit about Ruby, which I know pretty much nothing
> about.  I found it interesting, so figured I'd share here.  Enjoy!

I've been using ruby for about a year and a half now, and I love it. At
some point I should come in and do a talk on it, if someone else more
qualified doesn't step up.


> ----- Forwarded message from Bill Kelly -----
> Date: Wed, 07 Apr 2010 16:02:14 -0700
> From: Bill Kelly
> Subject: Re: [SDL] Off-Topic: Quake II Ported to HTML5
> To: SDL Development List <sdl@lists.libsdl.org>
> Mason Wheeler wrote:
> > Congratulations, you just discovered dynamic typing's dirty little secret.
> > It looks really cool in a demo, but it turns out real code hardly uses it at all.
> > Data has a type and tends to stay that type far more often than not, so
> > why not formalize that and gain the benefits of compile-time type checking
> > and static analysis tools?
> One thing several individuals who enjoy programming in ruby have
> observed about the language is that it "stays out of your way".
> Reflecting on a couple decades of programming in C and about
> half that for C++ , I still find it hard to pin down or quantify
> precisely why i feel more productive in dynamic languages.
> But I'd say that when a language really embraces its dynamicity,
> the gestalt is more than just the narrow focus on type
> declarations.
> I wish I had an SDL example to offer, so this could be more on-
> topic.
> But here's a database example, making use of an Object Relational
> Mapping library called Og.
> Almost ironically we are going to see some type declarations here,
> as the database columns themselves will be typed:
> class Address
>   property :name, String
>   property :company, String
>   property :dept, String
>   property :addr1, String
>   property :addr2, String
>   property :city, String
>   property :state, String
>   property :zip, String
>   property :country, String
>   belongs_to :order, Order
> end
> The above does an awful lot; I'll try to be brief.
> At compile time, we're defining an ordinary ruby class called
> Address ; however, also at compile time the "property" and
> "belongs_to" methods are being executed and doing some work.
> Neither the "property" nor "belongs_to" methods are part
> of Ruby; they've been added by the Og library.
> In ruby, there's not a lot of distinction between compile-
> time and run-time ; the full interpreter is available at all
> times, and one can define or modify classes or methods at
> any time.
> This level of dynamicity may sound alarming, but I enjoyed
> ruby's designer, matz, likening it to trusting the programmer
> to use dangerous tools:
>  | "open class" is so strong (often too strong), we can break things
>  | easily. In other word, Ruby trust you to give you sharp knives, where
>  | Python don't. From the Python point of view, it's wrong, I guess.
> Anyway.  At "compile-time" the statements in the Address class
> above end up both defining methods in the class, as well as
> linking the class into the Og library's checklist of which
> classes it will be managing as database tables.
> When the Og library is then started up at "run-time", like,
> for example:
>   Og.start(
>     :destroy => false,
>     :evolve_schema => true,
>     :store => :postgresql,
>     :name => 'database-name',
>     :user => 'db-user'
>   )
> It will examine its checklist of classes like Address above,
> which it knows about simply because such classes were encountered
> at compile-time and invoked Og's defining methods like
> "property", and it will examine their structure and generate
> the SQL / DDL necessary to realize the corresponding schema
> in the database.
> That's already pretty dynamic, but we're not done yet...
> Og has also imbued any class it manages with some additional
> on-the-fly run-time dynamicity.
> For example, we can say:
>   records = Address.find_all_by_city_and_state("Los Angeles", "CA")
>   records.each do |rec|
>     puts "#{rec.name} #{rec.company}"
>   end
> Now, with Address.find_all_by_city_and_state, we're calling
> a "class method" on Address which didn't even exist until now.
> But, like Smalltalk (messageNotUnderstood), Ruby provides a
> hook to handle messages sent to a class for which no existing
> method can be found to respond to the message.  (method_missing)
> So, Og imbues its managed classes with a method_missing
> implementation which looks at the method called, and if it
> matches a pattern like /find_(all_)?by_(\w+)(_(and|or)(\w+))*/
> will implement a method on the fly which performs the
> requested search on the appropriate columns.
> (And if the Og implementors chose, they could define said
> method on the class, such that next time it was called, it
> would execute directly as a method rather than virtually via
> the method_missing hook.)
> Powerful stuff.  Could give more examples, but I hope this helps
> illustrate that really dynamic languages offer a lot more power
> than just a narrow focus on type declarations.  (And we use it.)
> Regards,
> Bill
> ----- End forwarded message -----
> -- 
> -bill!
> Sent from my computer
> _______________________________________________
> vox mailing list
> vox@lists.lugod.org
> http://lists.lugod.org/mailman/listinfo/vox
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