Bug #5309

0.6.to_r != "0.6".to_r

Added by brixen (Brian Ford) 8 months ago. Updated 8 months ago.

[ruby-core:39484]
Status:Rejected Start date:09/13/2011
Priority:Normal Due date:
Assignee:- % Done:

0%
Category:-
Target version:-
ruby -v:-

Description

0.6.to_r != "0.6".to_r Is this a bug? $ ruby -v ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0] $ irb ruby-1.9.2-p290 :001 > 0.6.to_r => (5404319552844595/9007199254740992) ruby-1.9.2-p290 :002 > "0.6".to_r => (3/5) ruby-1.9.2-p290 :003 > a = "%.55f" % 0.6 => "0.5999999999999999777955395074968691915273666381835937500" ruby-1.9.2-p290 :004 > b = "%.55f" % "0.6".to_f => "0.5999999999999999777955395074968691915273666381835937500" ruby-1.9.2-p290 :005 > a == b => true Thanks, Brian

Related issues

duplicates ruby-trunk - Feature #1408: 0.1.to_r not equal to (1/10) Closed 04/26/2009

History

[ruby-core:39488]#1
Updated by naruse (Yui NARUSE) 8 months ago

  • Status changed from Open to Rejected
0.6.to_r is considered as a rational converted from a floating point number 0.5999999999999999777955395074968691915273666381835937500. "0.6".to_r is considered as Rational(6, 10). So they are slightly different number.

[ruby-core:39490]#2
Updated by marcandre (Marc-Andre Lafortune) 8 months ago

Use `Float#rationalize` instead of `to_r`, and you will get the same result as `String#to_r`. I've argued before that `Float#to_r` should be `Float#rationalize`, though.

[ruby-core:39496]#3
Updated by Anonymous 8 months ago

On Sep 12, 2011, at 2:06 PM, Brian Ford wrote: > 0.6.to_r != "0.6".to_r > > Is this a bug? Probably not because 0.6.to_r requires two conversions: decimal floating point to binary floating point to rational while "0.6".to_r only requires one conversion from decimal floating point to rational. In the first case, the intermediate value is not exactly 3/5 so the two sequences don't give you the same result. Gary Wright

[ruby-core:39497]#4
Updated by naruse (Yui NARUSE) 8 months ago

  • ruby -v changed from ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0] to -
2011/9/13 Marc-Andre Lafortune <ruby-core@marc-andre.ca>: > Use `Float#rationalize` instead of `to_r`, and you will get the same result as `String#to_r`. > I've argued before that `Float#to_r` should be `Float#rationalize`, though. It is http://redmine.ruby-lang.org/issues/1408 -- NARUSE, Yui  <naruse@airemix.jp>

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