Bug #2756: Issues with Math and Complex behavior on 1.9
http://redmine.ruby-lang.org/issues/show/2756

Author: Brian Ford
Status: Open, Priority: Normal
Target version: 1.9.2
ruby -v: ruby 1.9.2dev (2010-02-18 trunk 26704) [i386-darwin9.8.0]

This ticket aggregates several issues with Math methods on 1.9. There are related tickets that either have not yet or do not, in my opinion, resolve these issues in a satisfactory manner. (see http://redmine.ruby-lang.org/issues/show/1708, and related to the behavior of Math http://redmine.ruby-lang.org/issues/show/2189 and to 1.8 behavior http://redmine.ruby-lang.org/issues/show/2754)

1. There are behaviors that are inconsistent with 1.8

# On 1.8, the argument is coerced
$ ruby1.8.7 -v -e 'o = Object.new; def o.to_f; 0.5; end; p Math.atanh(o)'ruby 1.8.7 (2009-12-24 patchlevel 248) [i686-darwin9.8.0]
0.549306144334055

# On 1.9, the argement is not coerced
$ ruby1.9 -v -e 'o = Object.new; def o.to_f; 0.5; end; p Math.atanh(o)'
ruby 1.9.2dev (2010-02-18 trunk 26704) [i386-darwin9.8.0]
-e:1:in `atanh': can't convert Object into Float (TypeError)
        from -e:1:in `<main>'

Q. Should 1.9 coerce arguments to Math methods?

# On 1.8, an ArgmentError is raised
$ ruby1.8.7 -v -e 'p Math.atanh("str")'
ruby 1.8.7 (2009-12-24 patchlevel 248) [i686-darwin9.8.0]
-e:1:in `atanh': invalid value for Float(): "str" (ArgumentError)
        from -e:1

# On 1.9, a TypeError is raised
$ ruby1.9 -v -e 'p Math.atanh("str")'
ruby 1.9.2dev (2010-02-18 trunk 26704) [i386-darwin9.8.0]
-e:1:in `atanh': can't convert String into Float (TypeError)
        from -e:1:in `<main>'

Q. In this case, TypeError would appear more correct, so can the 1.8.7 behavior be changed? Also note that changing the 1.8.7 behavior would make it consistent with the behavior of atanh when requiring Complex (see http://redmine.ruby-lang.org/issues/show/2754)

2. There are behaviors that are inconsistent when requiring lib/complex.rb

# The original method raise a TypeError
$ ruby1.9 -v -e 'p Math.atanh(nil)'
ruby 1.9.2dev (2010-02-18 trunk 26704) [i386-darwin9.8.0]
-e:1:in `atanh': can't convert nil into Float (TypeError)
        from -e:1:in `<main>'

# The new method attempts an undefined operation and consequently raises a NoMethodError
$ ruby1.9 -v -rcomplex -e 'p Math.atanh(nil)'
ruby 1.9.2dev (2010-02-18 trunk 26704) [i386-darwin9.8.0]
lib/complex.rb is deprecated
/Users/brian/devel/ruby19/install/lib/ruby/1.9.1/cmath.rb:196:in `atanh': undefined method `real?' for nil:NilClass (NoMethodError)
        from -e:1:in `<main>'

The same behavior is observed when passing a String.

Q. Should the behavior of atanh after requiring lib/complex.rb be the same for non-Complex inputs as before?

Also, requiring lib/complex.rb on 1.9 causes a warning: "lib/complex.rb is deprecated". But this is not entirely true. As best as I can understand from http://redmine.ruby-lang.org/issues/show/1708, it was never decided whether complex.rb should require cmath.rb. It appears that there are some behaviors acquired via lib/complex.rb that are not deprecated. In that case, this warning is confusing and misleading.

Q. Is lib/complex.rb deprecated or not? If it is, why is it deprecated and not removed? 1.9 already removes many libraries. Why is this one special and allowed to cause such confusion?

Q. Is there a definitive document that explains the policy and behavior of Math and Complex in 1.9?


To summarize the questions in this ticket?

Q. Should 1.9 coerce arguments to Math methods?
Q. Can we change the 1.8.7 behavior when raising exceptions to be both internally consistent and consistent with the behavior of 1.9 (Note that numerous changes to the exception raised have already been made in 1.8.5 -> 1.8.6 -> 1.8.7, so this request is not without precedent.) (see http://redmine.ruby-lang.org/issues/show/2754)
Q. Should the behavior of atanh after requiring lib/complex.rb be the same for non-Complex inputs as before?
Q. Is lib/complex.rb deprecated or not? If it is, *why* is it deprecated and not removed?
Q. Is there a definitive document that explains the policy and behavior of Math and Complex in 1.9?

Thanks,
Brian


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