From: Joel VanderWerf <vjoel@...>
Date: 2009-05-16T04:13:33+09:00
Subject: Re: obj.attr(qualifier) = value -- possible?

Michael Schuerig wrote:
> I want to write a method that can be called like this
> 
>   obj.attr(qualifier) = value
> 
> So far, I don't see how to achieve this. I've tried
> 
> class C
>   def attr=(qualifier, value)
>     ...
>   end
> end
> 
> as well as
> 
> class D
>   def attr(qualifier)
>     Proxy.new(self, qualifier)
>   end
>   class Proxy
>     def =(value)
>       ...
>     end
>   end
> end
> 
> Neither is valid Ruby, apparently. Is there another, working way?
> 
> Michael
> 

I'm pretty sure that's impossible -- there is no #() method, or #()=. 
But there is #[]=, and you can adapt your Proxy approach to use it:

class D
   def attr
     Proxy.new(self)
   end
   def handle qualifier, value
     puts "handling #{qualifier.inspect}, #{value.inspect}"
   end

   class Proxy
     def initialize obj
       @obj = obj
     end
     def []=(qualifier, value)
       @obj.send(:handle, qualifier, value)
     end
   end
end

d = D.new
d.attr["some qualifier"] = "some value"

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407