[ruby-core:64568] [ruby-trunk - Bug #2121] [Closed] mathn/rational destroys Fixnum#/, Fixnum#quo and Bignum#/, Bignum#quo

Issue #2121 has been updated by Hiroshi SHIBATA.

Status changed from Assigned to Closed

mathn library is deprecated on trunk [Feature #10169]

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Bug #2121: mathn/rational destroys Fixnum#/, Fixnum#quo and Bignum#/, Bignu=
m#quo
https://bugs.ruby-lang.org/issues/2121#change-48497

* Author: Charles Nutter
* Status: Closed
* Priority: Normal
* Assignee: Keiju Ishitsuka
* Category: lib
* Target version:=20
* ruby -v: Any 1.8.6 or higher
* Backport:=20
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=3Dbegin
 I've known this for a while, but only now realized this is actually a terr=
ible bug.
=20
 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, th=
e 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 conse=
nt by the programmer.
=20
 When requiring 'mathn', Fixnum#/ and Bignum#/ are replaced with versions t=
hat return a fractional value ('quo') causing a core math operator to retur=
n not just a different type, but *a different value*.
=20
 No core library should be allowed to modify the return value of core numer=
ic 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'.
=20
 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 no=
t commonly-used operators.
=20
 The following code should not fail; Fixnum#/ should never return a value o=
f a different magnitude based on which libraries are loaded:
=20
 {{{
 require 'test/unit'
=20
 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
=20
   def test_with_mathn
     require 'mathn'
     assert_equal 0, 1/3
   end
 end
 }}}
=20
 But it does fail:
=20
 {{{
 ~/projects/jruby =E2=9E=94 ruby test_fixnum_math.rb=20
 Loaded suite test_fixnum_math
 Started
 .F
 Finished in 0.016003 seconds.
=20
   1) Failure:
 test_with_mathn(TestFixnumMath) [test_fixnum_math.rb:11]:
 <0> expected but was
 <1/3>.
=20
 2 tests, 2 assertions, 1 failures, 0 errors
 }}}
=3Dend




--=20
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