From: Yukihiro Matsumoto <matz@...>
Date: 2009-11-09T18:01:07+09:00
Subject: [ruby-core:26648] Re: [Bug #2346] Array(nil) fails after redefining NilClass.method_missing to throw NoMethodError

Hi,

In message "Re: [ruby-core:26628] [Bug #2346] Array(nil) fails after redefining NilClass.method_missing to throw NoMethodError"
    on Mon, 9 Nov 2009 01:56:47 +0900, Romulo Ceccon <redmine@ruby-lang.org> writes:

|Given the following script:
|
|  print "Array(nil) => ", Array(nil).inspect, "\n"
|  print "Array.try_convert(nil) => ", Array.try_convert(nil).inspect, "\n"
|  class NilClass
|    private
|    def method_missing(method, *args, &block)
|      raise NoMethodError
|    end
|  end
|  print "Array(nil) => ", Array(nil).inspect, "\n"
|  print "Array.try_convert(nil) => ", Array.try_convert(nil).inspect, "\n"
|
|Ruby 1.9.2dev returns this:
|
|  $ ruby -v
|  ruby 1.9.2dev (2009-11-08 trunk 25690) [i386-mswin32_90]
|
|  $ ruby nil_ary.rb
|  Array(nil) => []
|  Array.try_convert(nil) => nil
|  nil_ary.rb:6:in `method_missing': NoMethodError (NoMethodError)
|          from nil_ary.rb:9:in `Array'
|          from nil_ary.rb:9:in `<main>'

Because 1.9 actually calls the conversion method, where 1.8 checks
method existence by respond_to?  In other words, 1.9 respects duck
typing more thoroughly.  This one is a side effect.

If you don't want see exception raised, use super from method_missing,
or you can do like the following (not recommended):

  print "Array(nil) => ", Array(nil).inspect, "\n"
  print "Array.try_convert(nil) => ", Array.try_convert(nil).inspect, "\n"
  class NilClass
    private
    def method_missing(method, *args, &block)
      raise NoMethodError.new("undefined method #{method}", method), caller(1)
    end
  end
  print "Array(nil) => ", Array(nil).inspect, "\n"
  print "Array.try_convert(nil) => ", Array.try_convert(nil).inspect, "\n"
 
							matz.