From: Pierre Barbier de Reuille <p.barbierdereuille@...>
Date: 2006-01-08T01:23:01+09:00
Subject: Re: Iterator Fu Failing Me

ara.t.howard@noaa.gov a �crit :
> On Sat, 7 Jan 2006, James Edward Gray II wrote:
> 
>> I have a group of classes, all implementing a parse?() class method. 
>> Calling parse?(token) will return the constructed object, if it can be
>> parsed by this class, or false otherwise.
>>
>> I want to run a bunch of tokens through these classes, grabbing the
>> first fit.  For example:
>>
>>  elements = tokens.map do |token|
>>    ClassA.parse?(token) or
>>    ClassB.parse?(token) or
>>    ClassC.parse?(token)
>>  end
>>
>> That works.  Now can anyone give me a version of the middle section
>> that doesn't require I call parse?() 50 times?  I want something close
>> to:
>>
>>  elements = tokens.map do |token|
>>    [ClassA, ClassB, ClassC].find { |kind| kind.parse?(token) }
>>  end
>>
>> Except that I want the return result of parse?(), instead of the class
>> that took it.
> 
> 
> 
>   harp:~ > cat a.rb
> 
>   module Parser
>     module ClassMethods
>       def parse tokens, klasses
>         tokens.map{|token| catch('parse!'){ klasses.each{|klass|
> klass.parse! token}; nil}}
>       end
>       def parse! token
>         ret = parse?(token) and throw 'parse!', ret
>       end
>       def parse? token
>         return "<#{ token }> parsed by <#{ self }>" if token =~ self::RE
>       end
>     end
>     module InstanceMethods
>     end
>     def self::included other
>       other.module_eval{ extend ClassMethods and include InstanceMethods }
>     end
>     extend ClassMethods and include InstanceMethods
>   end

Could you explain this module ?

I think I can understand why you defined a module ClassMethods : to
include class methods and not only instace methods.

However, I don't understant why the InstanceMethods module ? What do you
expect with this module ? Is it just for symetry ?

Thanks !