From: "Paul A." <cyril.staff@...>
Date: 2010-04-30T19:50:09+09:00
Subject: Switching dynamically between methods (inside modules)

Hi,

I would like to allow a person object (instanced from a Person class) to
speak a language (which is a collection of public methods stored in
Language module):

>> class Person
>>   attr_accessor :current_language
>> 
>>   def quit
>>     # Unselect the current language, if any:
>>     @current_language = nil
>>   end
>> end

Suppose that languages are the following:

>> module Language
>>   module Japanese
>>     def konnichiwa
>>       "こんにちは！ (in #{@current_language} language)"
>>     end
>> 
>>     def sayounara
>>       "さようなら。 (in #{@current_language} language)"
>>     end
>>   end
>> 
>>   module French
>>     def bonjour
>>       "Bonjour ! (in #{@current_language} language)"
>>     end
>> 
>>     def au_revoir
>>       "Au revoir. (in #{@current_language} language)"
>>     end
>>   end
>> 
>>   module English
>>     def hello
>>       "Hello! (in #{@current_language} language)"
>>     end
>> 
>>     def bye
>>       "Bye. (in #{@current_language} language)"
>>     end
>>   end
>> end

Example of use:

person = Person.new

person.current_language # => nil
person.hello            # => may raise a nice no method error

person.current_language = :english
person.hello    # => "Hello! (from english instance variable)"
person.bonjour  # => may also raise a no method error
person.quit

person.current_language = :french
person.bonjour  # => "Bonjour ! (from french instance variable)"

As you can see, a language is such as a protocol. So a person can switch
on a specific protocol, but only one at a time.

For modular reasons, storing each language into a module is friendly. So
I think this way is the more logical Ruby way, isn't it.

So I would like to merge and unmerge dynamically module's methods (with
a kind of dynamic include) into the object... and then (for instance)
access them with person.public_send(). Thus, instance variables like
@current_language are still accessible from the new methods.

But, I believe that it is not possible to write something like this:

>> class Person
>>   # wrong code:
>>   include "Language::#{@current_language}" unless @current_language.nil?
>> end

According to you, what could be the best practice to do so?

Any comments and messages are welcome. Thank you.

Regards
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