From: Robert Dober <robert.dober@...>
Date: 2007-05-31T05:31:24+09:00
Subject: Re: #respond_to? not working for dynamically generated metho

On 5/30/07, James Edward Gray II <james@grayproductions.net> wrote:
> On May 30, 2007, at 9:57 AM, Maurice Gladwell wrote:
>
> > It would be interesting to see an implementation of James Edward
> > Gray's
> > suggestion above. ("You use an Extract Method refactoring to pull out
> > the matching logic into a separate private method and use that in
> > both implementations.")
>
> #!/usr/bin/env ruby -wKU
>
> class Test
>    def initialize(*fields)
>      @fields = fields.map { |f| f.to_s }
>    end
>
>    def find(*args)
>      "Performing query with args:\n#{args.inspect}"
>    end
>
>    def method_missing(meth, *args, &block)
>      if find_args = dynamic_finder?(meth)
>        find( find_args.first,
>              :conditions => find_args[1..-1].zip(args).
>                                              map { |n, v| "#{n} = '#
> {v}'"}.
>                                              join(" AND ") )
>      else
>        super
>      end
>    end
>
>    def respond_to?(*args)
>      super || dynamic_finder?(args.first)
>    end
>
>    private
>
>    def dynamic_finder?(method_call)
>      if method_call.to_s =~ /\Afind(_all)?_by_(\w+)\Z/
>        args =  [$1 ? :all : :first]
>        args += $2.split("_and_")
>        args if args[1..-1].all? { |f| @fields.include? f }
>      end
>    end
> end
>
> if __FILE__ == $PROGRAM_NAME
>    model = Test.new(:name, :age, :height, :weight)
>
>    p !!model.respond_to?(:find_by_name_and_height)
>    p !!model.respond_to?(:find_all_by_age)
>    p !!model.respond_to?(:find_all_by_race)
>
>    puts
>
>    puts model.find_by_name_and_height("James", "61 in.")
>    puts model.find_all_by_name_and_height
> end
>
> James Edward Gray II
>
>
>

This is very interesting, I just imagine that dynamic_finder does not
give consistent results depending on events outside the Ruby
program(*). Are you still happy with the semantics, instead of
respond_to? giving false negatives it gives false positives now.
A second issue was brought up by David,( I have no idea why he put a smiley ;)
You have created a dependency between method_missing and respond_to? I
really feel bad about this.

Robert

(*) or maybe by threading
-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw