From: Robert Klemme <shortcutter@...>
Date: 2007-03-16T18:15:07+09:00
Subject: Re: Anyone playing with higher order messaging in ruby?

On 15.03.2007 21:28, Rick DeNatale wrote:
> 2) mime content negotiation
> 
>   An action might be able to respond to a request with more than one
> mime-type.  An HTTP request can give a prioritized lists of mime-types
> which the client will accept.  The way to handle this negotiation in
> an action is to use the respond_to method you might have code in an
> action like:
> 
>    respond_to do |wants|
>            wants.html { redirect_to(person_list_url) }
>            wants.js
>            wants.xml  { render :xml => @person.to_xml(:include => 
> @company) }
>      end
> 
> What this code says is something like:
>     if the requester wants html redirect to the person_list_url
>     if the requester wants java script perform the normal rendering
> for javascript (such as look for an rjs template with the right name
> and render that)
>     etc.
> 
> It's kind of like a case statement, except what really happens also
> depends on which of those alternatives came first in the requests list
> of acceptable types.

That is no difference to case statements: with those, order matters as well:

 >> x="foo"
=> "foo"
 >> case x
 >> when /fo/; puts 1
 >> when /oo/; puts 2
 >> else puts 0
 >> end
1
=> nil
 >> case x
 >> when /oo/; puts 2
 >> when /fo/; puts 1
 >> else puts 0
 >> end
2
=> nil

I think the major difference (apart from syntactical aspects) is the 
execution time.  Of course this could also be mimicked with a case 
statement by returning a Proc but the Rails version looks much more elegant.

> It's good to read such carefully crafted code and understand the
> techniques and the possibilities, but I'd caution about getting too
> carried away with such things before you are ready, and most folks
> thing they are ready before they really are. <G>

Agreed. ;-)

Kind regards

	robert