Hi, I have been using rails to do some pilot applications now and I have often come accross the comment that Rails uses Ruby features to the maximum. I never could get what exactly are those things.However,one cool thing that I came accross was that new method names could be invented on models. Like '' UserDetails.find_by_email_id'' .Although this method is not defined in any scaffold code generated ( correct me here,if needed)I figure that Rails uses the "method_missing" feature of Ruby to trap this method invocation and somehow correctly generate an SQL query. Is there more like this? Also do other languages like python or perl not support this kind of reflection? Thanks Vivek _______________________________________________ Rails mailing list Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org http://lists.rubyonrails.org/mailman/listinfo/rails
On Fri, Dec 09, 2005 at 09:51:43AM +0530, Vivek Krishna wrote:> Is there more like this? Also do other languages like python or perl not > support this kind of reflection?Python supports trapping unknown method calls (via __getattr__); I''ve not worked out a way to make it look as neat as how it can be done in Ruby, though. - Matt
On Dec 8, 2005, at 9:21 PM, Vivek Krishna wrote:> Hi, > I have been using rails to do some pilot applications now and I > have often come accross the comment that Rails uses Ruby features > to the maximum. I never could get what exactly are those > things.However,one cool thing that I came accross was that new > method names could be invented on models. Like > ''UserDetails.find_by_email_id'' .Although this method is not defined > in any scaffold code generated ( correct me here,if needed)I figure > that Rails uses the "method_missing" feature of Ruby to trap this > method invocation and somehow correctly generate an SQL query. > Is there more like this? Also do other languages like python or > perl not support this kind of reflection?I''m sure other languages do this. Off the top of my head, here are some features: - Wrapping transactions in a block - The Routing code is a GeneratorGenerator which is pretty cool. Ruby code that creates ruby code... pretty deep stuff, though not yet Artificially Intelligent. - Mocks are a neat feature that take the place of Dependency Injection - Having converted ActiveRecord to PHP at one point (see phpontrax.com) I know that things like the acts_as_* genre of class methods are not possible in PHP. Generally, any class method called during the definition of a PHP class won''t work. Ruby is pretty amazing there. - Breakpoints are fabulous. They let you play with live objects, redefine classes on the fly etc. Duane Johnson (canadaduane)
> > I''m sure other languages do this. > > Off the top of my head, here are some features: > > - Wrapping transactions in a blockIs there any place I can get this? I mean i know i can always read code..but still I dont understand what transactions you mean here. - The Routing code is a GeneratorGenerator which is pretty cool.> Ruby code that creates ruby code... pretty deep stuff, though not yet > Artificially Intelligent.Rails generates a lot of code but I have to agree the routing code and logic works transparently It took me a while to figure out how those urls were converted to actions. Thanks again Vivek _______________________________________________ Rails mailing list Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org http://lists.rubyonrails.org/mailman/listinfo/rails
In python the metaprogramming is uglier but what you''d do is something
like this:
class whatever:
def __getattr__(self,name):
query_str = make_query_str(name)
class TempClass:
def __call__(): return do_sql_query(query_str)
return TempClass()
>From the user''s perspective the result is the same, except that of
course function calls require () in python. I''ve used this technique
to build object proxies and it works out well in practice.
You can also accomplish this using metaclasses, but it would be more
complicated (though also more efficient...). Essentially, at class
creation time, you''d query the database (it would take a trick to
delay this like rails does, but tricks are easy when you can
access/implement namespaces via dictionary-like objects) and bind a
set of methods which instantiated objects of that type would use.
Vivek: Python is similarly flexible to ruby but a lot of this "slick"
stuff is more explicit and IMHO more complicated to implement (see:
__metaclass__). Multiple inheritance and explicit metaclasses are a
valid representation for the ideas that ruby solves with it''s
"metaclasses", method_missing, modules, etc.
Brian