Float#to_d在哪里？

Question

有时我看到代码使用to_d.ruby文档甚至指出有一种Float#to_d方法.但是,它不在我的ruby(ruby 1.9.3p263 (2012-08-23 revision 36792)版本中.

1.9.3p263 :001 > "0.0".to_d
NoMethodError: undefined method `to_d' for "0.0":String
    from (irb):1
    from /home/iblue/.rvm/rubies/ruby-1.9.3-head/bin/irb:16:in `<main>'
1.9.3p263 :002 > 0.0.to_d
NoMethodError: undefined method `to_d' for 0.0:Float
    from (irb):2
    from /home/iblue/.rvm/rubies/ruby-1.9.3-head/bin/irb:16:in `<main>'
1.9.3p263 :003 > 0.to_d
NoMethodError: undefined method `to_d' for 0:Fixnum
    from (irb):3
    from /home/iblue/.rvm/rubies/ruby-1.9.3-head/bin/irb:16:in `<main>'

没有to_d中Float,String或Fixnum.这是怎么回事？

Answer 1

如您需要的文档示例中所述

require 'bigdecimal'
require 'bigdecimal/util'