Daysleeper

Class Variables in Ruby

Well much has been said about class variables in Ruby and how good and bad they are. When a C++/Java Programmer comes to Ruby, his search of static class variables begin immediately and unfortunately current Text on Ruby seems to suggest that, class variables are apt equivalents of static variables.

Answer is yes and no. When you use class variables, remember they are the same for all instance of the classes, even derived classes will reflect upon the same value and if you modify the class variables in one of those derived classes, it would be changed for all the other classes, which inherit the same parent. Got the picture?

Ok, Here is scary bit of code:

@@avar = 1
class A
  @@avar = "hello"
end
puts @@avar  # => hello

There is nothing special about code, if you look closely, because if you don’t define a class and declare class variables outside class definition, by default it gets hooked into Object class and since all the classes one way or the other end up inheriting from Object class, if you change the class variable declared at Object class scope in any of the classes, it would be reflected back in class variable held by Object class(bullshit, its the same variable)

Often, thats not.. what you want. Enter class instance variables, which are nice and dandy variables.. which are again avaialble to all the instances of the class and if you change the variable in one instance of the class, it would be reflected everywhere. But unlike class variables, they are not inherited.

Without much ado, here the sweet spot:

class A
  @foo = "bar"
  class << self; attr_accessor: foo; end
end
class B < A
end
p A.foo #=> bar
p B.foo #=> nil
B.foo = "blah"
p B.foo #=> blah

The overhead is, if you have to access them from instance methods of classes, then you will have to use self.class.foo

there are two approaches of mutlithreaded programming

For me, In any long running server app, there are only two rules of multithreaded programming:

• I don’t do it.


• I do 200% solid, multithreaded programming with proper test cases, unit tests and simulators to weed out all the race conditions. If i don’t do the above, its gonna suck. Its not a FPS game, that I would expect my users to simply restart.

Books I have been reading recently

Books I have been reading recently:

• The Mythical man-month :
  

  
  The book is quite nice and explains practises of software programmers. How Projects succeed or fail and stuff.
  



• Ajax in Action :
  

  
  I am reading it, so comments would follow.
  



• Surviving on Stupidity in 21st Century:
  

  
  A hilarious dilbert book about individhuals.
  



• Surely, You are joking Mr. Feynman :
  

  
  Call me that I was hiding under a rock, but I never really read the book and I done it recently.
  

fscking cool stuff from ActiveSupport

Some rails stuff from ActiveSupport

>> a = "Hemant Kumar"
=> "Hemant Kumar"
>> a.at(4)
=> "n"
>> a.from(4)
=> "nt Kumar"
>> a.first(4)
=> "Hema"
>> a.last(4)
=> "umar"
>> a = "2007/01/01 9:11:25PM"
=> "2007/01/01 9:11:25PM"
>> a.to_time
=> Mon Jan 01 21:11:25 UTC 2007
>> a.to_date
=> #<Date: 4908203/2,0,2299161>
>> a = "camels"
=> "camels"
>> a.pluralize
=> "camels"
>> a = "user_comments"
=> "user_comments"
>> a.camelize
=> "UserComments"
>> "UserComments".underscore
=> "user_comments"
>> "user_comments".dasherize
=> "user-comments"
>> "UserComments".demodulize
=> "UserComments"
>> "UserComments".tableize
=> "user_comments"
>> "UserComments".classify
=> "UserComment"
>> "UserComments".humanize
=> "Usercomments"
>> "UserComments".foreign_key
=> "user_comments_id"
>> "User".constantize
=> User
>> "user_comments".each_char {|char| print char}
=> nil
>> "640 <lol>".starts_with? 640
=> true
>> "640 <lol>".ends_with? "lol>"
=> true
>> "अ".is_utf8?
=> true
>> class Foobar
>>   cattr_reader :name
>>   def foo
>>     p "#{@name}"
>>   end
>> end
=> nil
>> foo = Foobar
=> Foobar
>> foo.name = "Hemant"
"NoMethodError: undefined method `name=' for Foobar:Class
  from (irb):45"
>> foo.name
=> nil
>> class << foo
>>   cattr_accessor :age
>> end
=> [:age]
>> foo.age = 10
=> 10
>> foo.age
=> 10
>> foo.class_variables
=> ["@@name"]
>> foo.instance_variables
=> ["@inheritable_attributes"]
>> class Blah
>>   class_inheritable_writer :age
>> end
=> [:age]
>> class Bleh < Blah
>> end
TypeError: superclass mismatch for class Bleh
  from (irb):80
>> class Beam
>> end
=> nil
>> class Blem
>> end
=> nil
>> " ".blank?
=> true
>> "       ".blank?
=> true
>> a = nil
=> nil
>> a.blank?
=> true
>> a = []
=> []
>> a.blank?
=> true
>> a = {}
=> {}
>> a.blank?
=> true
>> a = User.find(:all,:select => "id,login")
=> [#<User:0xb6f84128 ]
>> a.class
=> Array
>> a.index_by(&:id)
=> {71=>#<User:0xb6f84024>}
>> a.index_by(&:id).hash
=> -612671648
>> c = a.index_by(&:id)
=> {71=>#<User:0xb6f84024 @attributes={"id"=>"71"}}
>> c.class
=> Hash
>> a = [1,2,3,4]
=> [1, 2, 3, 4]
>> a.sum
=> 10
>> a = {:name => "Hemant Kumar",:age => 10}
=> {:name=>"Hemant Kumar", :age=>10}
>> a.to_xml
=> "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<hash>\n  <name>Hemant Kumar</name>\n  <age type=\"integer\">10</age>\n</hash>\n"
>> b = "<person><name>Hemant</name><age>10</age></persone>"
=> "<person><name>Hemant</name><age>10</age></persone>"
>> b = "<person><name>Hemant</name><age>10</age></person>"
=> "<person><name>Hemant</name><age>10</age></person>"
>> Hash.from_xml b
=> {"person"=>{"name"=>"Hemant", "age"=>"10"}}
>> c = Hash.from_xml b
=> {"person"=>{"name"=>"Hemant", "age"=>"10"}}
>> a
=> {:name=>"Hemant Kumar", :age=>10}
>> a.diff c
=> {:name=>"Hemant Kumar", :age=>10, "person"=>{"name"=>"Hemant", "age"=>"10"}}
>> a.stringify_keys
=> {"name"=>"Hemant Kumar", "age"=>10}
>> d = a.diff c
=> {:name=>"Hemant Kumar", :age=>10, "person"=>{"name"=>"Hemant", "age"=>"10"}}
>> d.symbolize_keys
=> {:name=>"Hemant Kumar", :person=>{"name"=>"Hemant", "age"=>"10"}, :age=>10}
>> a.reverse_merge c
=> {:name=>"Hemant Kumar", :age=>10, "person"=>{"name"=>"Hemant", "age"=>"10"}}
>> a = 23
=> 23
>> a.even?
=> false
>> a.odd?
=> true
>> a.multiple_of 23
"NoMethodError: undefined method `multiple_of' for 23:Fixnum
  from (irb):123"
>> a.multiple_of? 23
=> true
>> 1.ordinalize
=> "1st"
>> module Fleh
>> mattr_writer :age
>> end
=> [:age]
>> Fleh.age = 10
=> 10
>>

No cash to pay bills

Whenever I stay at home during afternoon, I would be afraid someone may come with a bill and I won’t have cash to pay him.

I hate ding dong in afternoon.

Things your uncle didn't tell you about rails 1.2

Hmm, well with new year all the rails programmers have been chattering away about rails 1.2 and how it will do laundry for them and get christmas presents too( href )

Here is something, where I would list gotchas and stupid things that can stop you from going full steam ahead:

• Take a deep breadth and accept that memcache session handler is broken in development mode. As a quick fix you can use pstore for session storage in development mode. Update: Turns out that I was a complete idiot and was storing entire model in session and since now with Rails 1.2, only model which is required in the current controller context is reloaded in development mode, I didn’t have class definition for model in entire app and hence all the funny errors. just doing a require 'user' in application.rb fixed the issue. Cheers to Rails core team for helping me out on IRC.

• Now, rails reloads all your classes/modules for each new requests in development mode. Well, so what, its been doing that for years. So here is catch, it does this for /lib and /vendor/plugins also. And sometimes this can cause quite some trouble.
  http://dev.rubyonrails.org/ticket/6738
  So the simplest solution is to put this in your environment.rb file:
  

    config.load_once_paths = ["#{RAILS_ROOT}/lib"]

  
  Now, what it does is, it forces modules/classes defined in /lib to load only once.


• Well, rails routes are now a lot more stricter and doesn’t do too many assumptions. For example:
  

  >> rs.recognize_path "/forums/index"
  => {:controller=>"forums", :action=>"index"}
  >> rs.recognize_path "/forums"
  => {:controller=>"forums", :action=>"index"}
  >> rs.recognize_path "/forums/index/foo"
  => {:controller=>"forums", :action=>"index", :id=>"foo"}
  >> rs.recognize_path "/forums/index/foo.bar"
  ActionController::RoutingError: no route found to match "/forums/index/foo.bar" with {}
  >> 

  
  Well as you can see, params[:id] doesn’t like parameters with dots anymore and you must set an explicit route for this:
  

    map.connect('/forums/index/:id',
                :controller => 'forums',
                :action => 'index',
                :id => /.*/)

  
  Update: Please note, a better regexp would be required to properly match the ID, because otherwise it would gobble up everything after index. Its eager matching you see!!


• How to upgrade yourself:
  

  
  gem install rails --source http://gems.rubyonrails.org --include-dependencies
  

  
  And go to your project directory and do
  

  
  rake rails:update
  

  
  to update scipts/javascript/css rails generated for you.


• Update : with Rails 1.1.6, when you say request.domain you would normally get just the domain name but with rails 1.2.1 both request.host and request.host return the same thing by default. It means you will have to resort to these sort of ugly hacks:
  

    def get_subdomain url
      domain_string = url.split("://").last
      domain_array = domain_string.downcase.split('.')[0..1]
      country_codes = %w[au br ca cn fr de hk in it jp kr mx mg es tw uk us]
      country = domain_array.find { |x| country_codes.include? x}
      return country
    end

• There are quite few other stuffs and you should see:
  [1]
  http://weblog.rubyonrails.org/2006/11/23/rails-1-2-release-candidate-1
  [2] http://weblog.rubyonrails.org/2006/11/26/1-2-new-in-activerecord
  [3]
  http://weblog.rubyonrails.org/2006/11/26/1-2-new-in-actionpack
  [4] http://weblog.rubyonrails.org/2006/11/26/1-2-new-in-activesupport