Bug #5158: to_ary not respecting respond_to?

• Status: Closed
• Assignee: nobu (Nobuyoshi Nakada)
• Target version: -
• ruby -v: -

[zenspider (Ryan Davis)]

class BadProxyObject
def initialize
@p = Object.new
def @p.to_ary
raise "I should never be called"
end
end

def respond_to?(*a)
p :bad_respond_to? => a
false
end

def method_missing(msg, *)
p :bad_method_missing => msg
@p.send msg
end
end

[[BadProxyObject.new]].flatten

{:bad_method_missing=>:to_ary}

Exception `RuntimeError' at wtf.rb:6 - I should never be called

wtf.rb:6:in `to_ary': I should never be called (RuntimeError)

from wtf.rb:17:in `method_missing'

from wtf.rb:21:in `flatten'

from wtf.rb:21:in `'

Extra Info: http://tenderlovemaking.com/2011/06/28/til-its-ok-to-return-nil-from-to_ary/

[naruse (Yui NARUSE)]

• Status changed from Open to Assigned
• Assignee set to nobu (Nobuyoshi Nakada)

[nobu (Nobuyoshi Nakada)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r32855.
Ryan, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• vm_eval.c (check_funcall): try respond_to? first if redefined.
  [Bug #5158]

[aprescott (Adam Prescott)]

And I've just seen that http://redmine.ruby-lang.org/issues/5158 has been
opened and closed. Too slow, I guess.

[aprescott (Adam Prescott)]

On Thu, Aug 4, 2011 at 11:37 PM, Ryan Davis [e-mail]:

Extra Info:
http://tenderlovemaking.com/2011/06/28/til-its-ok-to-return-nil-from-to_ary/

Someone made a comment on that post linking to
http://yehudakatz.com/2010/01/02/the-craziest-fing-bug-ive-ever-seen/ which
explains, specifically for Array#flatten:

---

In Ruby 1.8, the process is essentially the following:

if obj.respond_to?(:to_ary)
obj.send(:to_ary)
else
obj
end

In Ruby 1.9, it was changed to:

begin
obj.send(:to_ary)
rescue NoMethodError
obj
end

---

I'm not sure why that changed happened, but at least that seems to be the
source of the behaviour.

On Aug 5, 2011, at 6:06 AM, Adam Prescott wrote:

I'm not sure why that changed happened, but at least that seems to be the source of the behaviour.

I believe it happened because respond_to? is unreliable in the presence of
method_missing unless a lot of care is taken, and that care is rarely taken.

Michael Edgar
[e-mail]
http://carboni.ca/