From: Stefano Crocco <stefano.crocco@...>
Date: 2007-03-15T23:54:46+09:00
Subject: Re: What does this do? :

Alle gioved� 15 marzo 2007, jko170 ha scritto:
> Looking at this piece of code, what does the colon do?
>
> def partner_to(user)
>     raise ArgumentError unless user
>     user.id == recipient_id ? sender : recipient
>  end
>
> I got the code from this rails post:
> http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/7fdccd
>dde9b97ffc/6112294580b9e0ce?lnk=gst&q=internal+mail&rnum=1#6112294580b9e0ce
>
> I'm just asking because I've never seen the colon used before.

This is a shortcut for
if user.id == recipient_id ? then sender
else recipient
end

What comes before the ? is the condition (not to confuse with the ? which ends 
the name of predicate methods: array.empty? do_something : do_something_else 
won't work, array.empty? ? do_something : do_something_else will), after 
the ? and before the : there's the action to take if the condition is true 
and after the : what to do if it's false.

Stefano