[ruby-core:25644] [Bug #2121] mathn/rational destroys Fixnum#/, Fixnum#quo and Bignum#/, Bignum#quo

Bug #2121: mathn/rational destroys Fixnum#/, Fixnum#quo and Bignum#/, Bignum#quo
http://redmine.ruby-lang.org/issues/show/2121

Author: Charles Nutter
Status: Open, Priority: Normal
ruby -v: Any 1.8.6 or higher

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
}}}


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