From: "Sandor Szücs" <sandor.szuecs@...>
Date: 2013-01-06T20:41:12+09:00
Subject: Re: respond_to_missing?

On 1/5/13 12:42 PM, Intransition wrote:
> Thank you Jan and Sandor. That is basically what I thought, but I had 
> recently become confused b/c of this:
> 
>   https://bugs.ruby-lang.org/issues/5759 
> 
> If you read toward the bottom of this thread, there is a case that seems 
> contradictory. I still don't get it.
> 

The difference of respond_to? and respond_to_missing? is that you can
get a Method object using Kernel#method(sym) if a method will be
dynamically implemented using method_missing.

Here again the example:
 13 class Bar1
 14     def respond_to_missing? *args
 15       true
 16     end
 17     def method_missing(*args, &blk)
 18       p args
 19     end
 20 end
 21
 22 class Baz1
 23     def respond_to? *args
 24       true
 25     end
 26
 27     def method_missing(*args, &blk)
 28       p args
 29     end
 30 end

# get the method:
irb:0> Bar1.new.method :foo
=> #<Method: Bar1#foo>

# do not get the method:
irb:0> Baz1.new.method :foo
NameError: undefined method `foo' for class `Baz1'
        from (irb):17:in `method'
        from (irb):17
        from /.../.rvm/rubies/ruby-1.9.3-p362/bin/irb:16:in `<main>'


In your example you define: "#to_ary() is not created dynamically nor
defined static"

class TransBaz1
  def method_missing(s)
    s
  end

  def respond_to_missing?(s, x)
    return false if s == :to_ary
    true
  end
end


irb:0> TransBaz1.new.method :to_ary
NameError: undefined method `to_ary' for class `TransBaz1'
        from (irb):45:in `method'
        from (irb):45
        from /.../.rvm/rubies/ruby-1.9.3-p362/bin/irb:16:in `<main>'
irb:0> TransBaz1.new.method :foo
=> #<Method: TransBaz1#foo>

You can not get Method object :to_ary using Kernel#method, but you can
get :foo.
-- 
All the best, Sandor Szücs