From: "headius (Charles Nutter)" <headius@...>
Date: 2012-11-17T19:16:07+09:00
Subject: [ruby-core:49484] [ruby-trunk - Bug #2121] mathn/rational destroys Fixnum#/, Fixnum#quo and Bignum#/, Bignum#quo


Issue #2121 has been updated by headius (Charles Nutter).


I sympathize with the desire to avoid breaking backward compatibility, but the idea that "10 / 2" is the wrong way and you should instead use "10.div(2)" is pretty anti-Ruby. This is terribly surprising and certainly not what any user would expect. I would suggest that a new method be added to Integer for the variable behavior...something like #ratio or #fraction.

Another example of why this sucks, from a Ruby implementer perspective...

In JRuby, the basic math operations are recognize and optimized for better performance...all except #/ because of the mathn problem. Silly, isn't it?
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Bug #2121: mathn/rational destroys Fixnum#/, Fixnum#quo and Bignum#/, Bignum#quo
https://bugs.ruby-lang.org/issues/2121#change-33015

Author: headius (Charles Nutter)
Status: Assigned
Priority: Normal
Assignee: keiju (Keiju Ishitsuka)
Category: lib
Target version: 
ruby -v: Any 1.8.6 or higher


=begin
 I've known this for a while, but only now realized this is actually a terrible bug.
 
 The mathn library replaces Fixnum#/ and Bignum#/ causing them to return a different value. When the result of a division is not an integral value, the default versions will return 0. I can think of many algorithms that would use this expectation, and most other languages will not upconvert integral numeric types to floating-point or fractional types without explicit consent by the programmer.
 
 When requiring 'mathn', Fixnum#/ and Bignum#/ are replaced with versions that return a fractional value ('quo') causing a core math operator to return not just a different type, but *a different value*.
 
 No core library should be allowed to modify the return value of core numeric operators, or else those operators are worthless; you can't rely on them to return a specific value *ever* since someone else could require 'mathn' or 'rational'.
 
 Note also that 'rational' destroys Fixnum#quo and Bignum#quo. This is also a bug that should be fixed, though it is less dangerous because they're not commonly-used operators.
 
 The following code should not fail; Fixnum#/ should never return a value of a different magnitude based on which libraries are loaded:
 
 {{{
 require 'test/unit'
 
 class TestFixnumMath < Test::Unit::TestCase
   # 0 to ensure it runs first, for illustration purposes
   def test_0_without_mathn
     assert_equal 0, 1/3
   end
 
   def test_with_mathn
     require 'mathn'
     assert_equal 0, 1/3
   end
 end
 }}}
 
 But it does fail:
 
 {{{
 ~/projects/jruby ��� ruby test_fixnum_math.rb 
 Loaded suite test_fixnum_math
 Started
 .F
 Finished in 0.016003 seconds.
 
   1) Failure:
 test_with_mathn(TestFixnumMath) [test_fixnum_math.rb:11]:
 <0> expected but was
 <1/3>.
 
 2 tests, 2 assertions, 1 failures, 0 errors
 }}}
=end



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