From: Rob Biedenharn <Rob@...>
Date: 2006-06-05T22:58:37+09:00
Subject: Re: Why doesn't method_missing affect respond_to?

On Jun 5, 2006, at 8:23 AM, Tim Hunter wrote:

> Pat Maddox wrote:
>> Take this class:
>>
>> class Foo
>>   def method_missing(m, *args)
>>     m.to_s
>>   end
>> end
>>
>> irb(main):006:0> Foo.new.foo
>> => "foo"
>> irb(main):007:0> Foo.respond_to? :foo
>> => false
>>
>> This obviously just returns the name of any method that doesn't exist
>> for the object.  So if you can send the object any message and get a
>> result, why doesn't it respond_to those messages?
>>
>> Pat
>
> The respond_to method can't know what method_missing is doing with
> missing methods, so it's the up to the class author to provide a  
> version
> of respond_to that agrees with method_missing.

More to the point, if you do this:
# foo.rb
class Foo
   def method_missing(m, *args)
     eval "def self.#{m}; '#{m}'; end"
     self.__send__(m)
   end
end

__END__

irb(main):001:0> require 'foo'
=> true
irb(main):002:0> f = Foo.new
=> #<Foo:0x1cd438>
irb(main):003:0> f.respond_to? :foo
=> false
irb(main):004:0> f.foo
=> "foo"
irb(main):005:0> f.respond_to? :foo
=> true
irb(main):006:0>

You've now defined a 'foo' method and further invocations of f.foo  
will go to the newly minted method rather than method_missing each time.

-Rob