From: "Carlo E. Prelz" <fluido@...>
Date: 2013-01-17T04:07:48+09:00
Subject: Re: Handling library versions

	Subject: Handling library versions
	Date: Thu 17 Jan 13 03:50:20AM +0900

Quoting Melanie Koller (lists@ruby-forum.com):

> I am trying to implement a library that provides an unified way to
> communicate to a server which is changing its API calls from version to
> version. I plan to implement it that way:
> 
> connect.rb:
> 
> class Connect
>     def self.getConn(params)
>         case params[:version]
>             when '4.0' then return Connect4.new(params)
>             when '5.0' then return Connect5.new(params)
>             else 'Version not supported.'
>         end
> 
>     end
> end
> 
> class Connect4
>     def initialize(params)
>         # Code for v4.
>     end
> end
> 
> class Connect5
>     def initialize(params)
>         # Code for v5.
>     end
> end

One of the advantages of object orientation is inheritance - ideal in
your case. I would do something like:

class Connect
  def Connect::get_conn(params)
    case params[:version]
      when '4.0' 
        return Connect4::new(params)
      when '5.0' 
        return Connect5::new(params)
      end	
    end   
    raise "Version #{params[:version]} not supported."
  end
  
  def generic_func
    ..
  end  
end
 
class Connect4 < Connect
  def initialize(params)
    # Code for v4.
  end

  def v4_specific_func
    ..
  end  
end

class Connect5 < Connect
  def initialize(params)
    # Code for v5.
  end

  def v5_specific_func
    ..
  end  

  def generic_func
    # overloads generic one
  end   
end
         
The advantage is that instances of both Connect4 and Connect5 also
respond to methods defined in Connect. You can thus neatly divide
between things that are unique of each version, and things that are
common among versions.

Carlo

-- 
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