[Chicago Area Ruby Group] Functor

[chicagogroup-members-list at rubyforge.org]

chicagogroup-members-list at rubyforge.org wrote:
> Wow. Um, can you elaborate a bit on that, maybe with a little bit of
> code? I think I might see what you're driving at, but I'm not quite
> there.

Given the following definition of a Functor:

   class Functor
     def initialize(&func)
       @func = func
     end
     def method_missing(op, *args)
       @func.call(op, *args)
     end
   end

Pretend I have a method called redirect that I am trying to test:

   def redirect(url, sys=Kernel)
     #
     # code here that writes out an HTTP header
     # that causes the redirect to url
     #

     # my header has been written so kill the script:
     sys.exit
   end

Here's my test method:

   def test_redirect__exit
     exited = false
     sys = Functor.new { |meth, *args|
       exited = true if meth == :exit
     }
     redirect('test/url.html', sys)
     assert(exited)
   end

Normally I would have created my own mock object instead and defined the 
test method like so:

   def test_redirect__exit
     sys = Object.new
     def sys.exit
        @exited = true
     end
     def sys.exited?
        @exited || false
     end
     redirect('test/url.html', sys)
     assert(sys.exited?)
   end

Not nearly as clean. This example is admittedly contrived, but I think 
it gives you an idea of how you could use a Functor as a Mock object. 
I'm sure there are a ton of other uses, but this is what came to mind.

Pretty cool use of method missing.

--
John