Backport #8958: Rational#to_d don't match documentation

• Status: Closed
• Assignee: nagachika (Tomoyuki Chikanaga)

[ejfinneran (E.J. Finneran)]

The documentation states that Rational#to_d (added by BigDecimal) has an optional parameter to limit the precision. However, that parameter is not optional as implemented.

http://www.ruby-doc.org/stdlib-2.0.0/libdoc/bigdecimal/rdoc/Rational.html

╰─○ ruby -v
ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.5.0]
╰─○ irb
2.0.0p247 :001 > require 'bigdecimal'
=> true
2.0.0p247 :002 > require 'bigdecimal/util'
=> true
2.0.0p247 :003 > 3.to_r.to_d
ArgumentError: wrong number of arguments (0 for 1)
from /Users/ej/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/bigdecimal/util.rb:98:in to_d' from (irb):3 from /Users/ej/.rvm/rubies/ruby-2.0.0-p247/bin/irb:16:in '
2.0.0p247 :004 > 3.to_r.to_d(1)
=> #BigDecimal:7ffc8c8afaa8,'0.3E1',9(36)

[zzak (zzak _)]

• Status changed from Open to Assigned

It seems the documentation is wrong, the implementation is a required argument: https://github.com/ruby/ruby/blob/trunk/ext/bigdecimal/lib/bigdecimal/util.rb#L119

I have asked for feedback from murata-san to confirm this spec in BigDecimal.

Thank you for finding this bug!

[zzak (zzak _)]

Still looking into this one E.J. thanks for your patience.

[mrkn (Kenta Murata)]

I think this is a bug of Rational#to_d. I'll fix it.

[marcandre (Marc-Andre Lafortune)]

@mrkn (Kenta Murata) I'm not sure it would make sense to have a default precision here... Is there a default precision anywhere in the BigDecimal library?

[mrkn (Kenta Murata)]

@marcandre (Marc-Andre Lafortune) Yes. We cannot determine a default precision for a rational number generally. I think I confused when I replied #3.

So this issue can be closed.

[zzak (zzak _)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r43669.
E.J., thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• ext/bigdecimal/lib/bigdecimal/util.rb: [DOC] Document the required
  +precision+ argument for Rational#to_d [Bug #8958]
  -This line, and those below, will be ignored--

M ChangeLog
M ext/bigdecimal/lib/bigdecimal/util.rb

[nagachika (Tomoyuki Chikanaga)]

• Status changed from Closed to Assigned
• Backport set to 1.9.3: DONTNEED, 2.0.0: REQUIRED

Hi,

There are still examples of Rational#to_d without arguments in documentation at call-seq section and sample code.

[zzak (zzak _)]

• Assignee changed from zzak (zzak _) to nagachika (Tomoyuki Chikanaga)

@nagachika (Tomoyuki Chikanaga) good catch, i removed the incorrect call-seq in r43672: https://github.com/ruby/ruby/commit/62d3853

I will assign it to you for backporting, thanks!

[nagachika (Tomoyuki Chikanaga)]

• Status changed from Assigned to Closed

This issue was solved with changeset r43678.
E.J., thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• ext/bigdecimal/lib/bigdecimal/util.rb: [DOC] remove example of
  Rational#to_d without argument. [Bug #8958]

[nagachika (Tomoyuki Chikanaga)]

• Tracker changed from Bug to Backport
• Project changed from Ruby master to Backport200
• Category deleted (doc)
• Status changed from Closed to Assigned

[nagachika (Tomoyuki Chikanaga)]

• Status changed from Assigned to Closed

This issue was solved with changeset r44314.
E.J., thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

merge revision(s) 43669,43672,43678: [Backport #8958]

* ext/bigdecimal/lib/bigdecimal/util.rb: [DOC] Document the required
  +precision+ argument for Rational#to_d [Bug #8958]

* ext/bigdecimal/lib/bigdecimal/util.rb: [DOC] +precision+ is required

* ext/bigdecimal/lib/bigdecimal/util.rb: [DOC] remove example of
  Rational#to_d without argument. [Bug #8958]