Bug #19004: Complex can be nested by Complex.polar

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 3.1.2
• Backport: 2.7: REQUIRED, 3.0: REQUIRED, 3.1: DONE

[msnm (Masahiro Nomoto)]

Complex.polar with one argument can return a "nested" Complex instance, whose real part is also a Complex one.

puts RUBY_DESCRIPTION
# ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]

p Complex.polar(1+0i)
# ((1+0i)+0i)

p 5.times.inject(1) { |num, _| Complex.polar(num) }
# (((((1+0i)+0i)+0i)+0i)+0i)

In Ruby < 2.7 , it simply raises an error when the argument is an instance of Complex (i.e. obj.real? == false).

puts RUBY_DESCRIPTION
# ruby 2.6.10p210 (2022-04-12 revision 67958) [x86_64-linux]

p Complex.polar(1+0i)
# TypeError (not a real)

[stevegeek (Stephen Ierodiaconou)]

I thought to try fixing this issue as a first contribution to Ruby. I have a proposed fix here https://github.com/ruby/ruby/pull/6568

Details are on the PR, but in summary, I believe that the ability to pass a Complex as the abs argument is the expected behaviour (given other methods on Complex also accept Complex value as long as they are real, in the sense they have a zero imaginary part). However Complex.polar with a single argument creates the new Complex without first extracting the real part of the argument, so Complex.polar(1+0.0i).real => (1+0i)

The propose fix simply ensures that the single argument case is handled in the same way as the 2 argument case, so Complex.polar(1+0.0i).real => 1

[nobu (Nobuyoshi Nakada)]

• Backport changed from 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN to 2.7: REQUIRED, 3.0: REQUIRED, 3.1: REQUIRED

[stevegeek (Stephen Ierodiaconou)]

• Status changed from Open to Closed

Applied in changeset git|54cad3123a07583c90e85bcfc55ebd87124c1250.

---

[Bug #19004] Complex.polar handles complex singular abs argument

Complex.polar accepts Complex values as arguments for the polar form as long
as the value of the complex has no imaginary part (ie it is 'real'). In
f_complex_polar this is handled by extracting the real part of the arguments.
However in the case polar is called with only a single argument, the absolute
value (abs), then the Complex is created without applying a check on the type
of abs, meaning it is possible to create a Complex where the real part is itself
an instance of a Complex. This change removes the short circuit for the single
argument case meaning the real part extraction is performed correctly
(by f_complex_polar).

Also adds an example to spec/ruby/core/complex/polar_spec.rb to check that
the real part of a complex argument is correctly extracted and used in the
resulting Complex real and imaginary parts.

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.7: REQUIRED, 3.0: REQUIRED, 3.1: REQUIRED to 2.7: REQUIRED, 3.0: REQUIRED, 3.1: DONE

ruby_3_1 597ce7966c38e4f7fc7368a860ac2d056de794ba merged revision(s) 54cad3123a07583c90e85bcfc55ebd87124c1250.