Issue #9170 has been updated by mrkn (Kenta Murata). Category set to core Status changed from Open to Feedback Target version set to next minor It's not a bug. Do you want to introduce Numeric#nan? method to resolve this problem? If so, this issue should be in Feature tracker. Please tell us how do you think. ---------------------------------------- Bug #9170: Math.sqrt returns different types when mathn is included; breaks various gems - this bug can be reproduced in Ruby 1.8 as well https://bugs.ruby-lang.org/issues/9170#change-43760 Author: kranzky (Jason Hutchens) Status: Feedback Priority: Normal Assignee: Category: core Target version: next minor ruby -v: ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.2.1] Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN Math.sqrt() usually returns a Float or throws an exception. Some gems rely on this behaviour (e.g. by calling nan? on the results of a calculation that includes a sqrt). After requiring mathn, Math.sqrt() returns an Integer in some cases (when the results of the sqrt would be a whole number). Here is a transcript that demonstrates the problem: $ rvm use ree Using /Users/jason/.rvm/gems/ree-1.8.7-2012.02 $ ruby -v ruby 1.8.7 (2012-02-08 MBARI 8/0x6770 on patchlevel 358) [i686-darwin12.1.0], MBARI 0x6770, Ruby Enterprise Edition 2012.02 $ ruby -e "puts Math.sqrt(4).nan?" false $ ruby -e "require 'mathn'; puts Math.sqrt(4).nan?" -e:1: undefined method `nan?' for 2:Fixnum (NoMethodError) $ rvm use 1.9.3 Using /Users/jason/.rvm/gems/ruby-1.9.3-p448 $ ruby -v ruby 1.9.3p448 (2013-06-27 revision 41675) [x86_64-darwin12.2.0] $ ruby -e "puts Math.sqrt(4).nan?" false $ ruby -e "require 'mathn'; puts Math.sqrt(4).nan?" -e:1:in `<main>': undefined method `nan?' for 2:Fixnum (NoMethodError) $ rvm use 2.0 Using /Users/jason/.rvm/gems/ruby-2.0.0-p247 $ ruby -v ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.2.1] $ ruby -e "puts Math.sqrt(4).nan?" false $ ruby -e "require 'mathn'; puts Math.sqrt(4).nan?" -e:1:in `<main>': undefined method `nan?' for 2:Fixnum (NoMethodError) $ rvm use jruby Using /Users/jason/.rvm/gems/jruby-1.7.4 $ ruby -v jruby 1.7.4 (1.9.3p392) 2013-05-16 2390d3b on Java HotSpot(TM) 64-Bit Server VM 1.6.0_51-b11-457-11M4509 [darwin-x86_64] $ ruby -e "puts Math.sqrt(4).nan?" false $ ruby -e "require 'mathn'; puts Math.sqrt(4).nan?" NoMethodError: undefined method `nan?' for 2:Fixnum (root) at -e:1 Here is a discussion of how the bug manifests itself: https://github.com/olbrich/ruby-units/pull/48 Inclusion of mathn causes issues in RGeo, Alchemist, ActiveShipping and pry-rails -- http://bugs.ruby-lang.org/