From: Mike Papper <bodarotech@...>
Date: 2009-12-08T11:02:02+09:00
Subject: Re: Use of extend <module> from within a Class

Hi and thanks for explaining the helper method. I understand whats going 
on except for

master_helper_module.module_eval

-what is master_helper_module ? (Presumably it has the effect of 
"include ModuleName - but how that makes self.class.XYZ work is still 
not understood).

----------------
Back to the UrlWriter module...

I did some tests and noticed that self.included is not called when a 
module is extended (versus included). For UrlWriter, this means that 
this code doesnt get executed:
    def self.included(base) #:nodoc:
      ActionController::Routing::Routes.install_helpers(base)
      base.mattr_accessor :default_url_options
      base.default_url_options ||= default_url_options
    end

I changed my code to explicitly call that method after I extended, ala:
def self.staticmethod
    extend ActionController::UrlWriter
    ActionController::UrlWriter.included(self) # the class
    self.default_url_options = {} # doesnt seem to do much

but still this line from UrlWriter.url_for fails:

  self.class.default_url_options.merge(options)

As you said, self.class refers to Class so I dont see how that line 
works when the module is included as a helper. Can you explain this??

Mike

Rick Denatale wrote:
> On Mon, Dec 7, 2009 at 4:26 PM, Mike Papper <bodarotech@gmail.com> 
> wrote:
>> helper but cannot really make any sense of it.
> MyController < ActionController::Base
>    include UrlWriter  # include not extend
> end
> 
> If you read the code in actionpack/lib/action_controller/helpers.rb it
> really isn't that hard to see what's going on
> 
> if in the controller you write say
> 
>    helper :url_writer
> 
> then the helper method takes the case branch for a symbol. which is:
> 
>               file_name  = arg.to_s.underscore + '_helper'
>               class_name = file_name.camelize
> 
>               begin
>                 require_dependency(file_name)
>               rescue LoadError => load_error
>                 requiree = / -- 
> (.*?)(\.rb)?$/.match(load_error.message).to_a[1]
>                 if requiree == file_name
>                   msg = "Missing helper file helpers/#{file_name}.rb"
>                   raise LoadError.new(msg).copy_blame!(load_error)
>                 else
>                   raise
>                 end
>               end
> 
>               add_template_helper(class_name.constantize)
> 
> So it computes a file name from the argument, in this case
> "url_writer.rb", and a class (actually a Module) name "UrlWriter"
> 
> Then require dependency loads the file if necessary, and finally.
> 
> class_name.constantize turns teh class name into the actual module,
> and passes it as the argument to add_template_helper which is defined
> above as:
> 
>       def add_template_helper(helper_module) #:nodoc:
>         master_helper_module.module_eval { include helper_module }
>       end
> 
> So it is effectively the same thing as what I first wrote.
> 
> --
> Rick DeNatale
> 
> Blog: http://talklikeaduck.denhaven2.com/
> Twitter: http://twitter.com/RickDeNatale
> WWR: http://www.workingwithrails.com/person/9021-rick-denatale
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