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Ruby should do X!
Why does ruby’s comparison with floats fail?
gems fail to load in 1.9.1
unicode characters are not found by \w in 1.9
here is a list comparing some
Instructions on how to submit a patch
Sometimes floats in Ruby do funky things.
Example of odd behavior:
>> (2.0-1.1) == 0.9 => false
Why? Because floats are by default slightly imprecise
This is not Ruby’s fault, but floating point numbers in general suffer from this type of rounding error, because they’re limited to x number of bytes, and, in general, cannot store decimal number perfectly.
Your options when you run into this:
assert_in_delta((1.1-0.9), 0.2, 0.0001) # passes
>> require 'bigdecimal' >> (BigDecimal.new("1.1") - BigDecimal.new("0.9")) == 0.2 => true
>> a = Rational(11, 10) - Rational(9, 10) # 11/10 - 9/10 => (1/5) >> a == 0.2 => true
What’s really going on here:
>> 1.1 => 1.1 # in reality this probably doesn't equal exactly 1.1 deep down--but it's equal to 1.1's default so ruby 1.9.2 will display it as 1.1 > 0.9 => 0.9 > 1.1-0.9 => 0.20000000000000007 # now ruby 1.9.2 notices that "this 0.2 is not the same as the default float for 0.2" so it displays its full version to remind us of this fact.
How can I make them pretty (misleadingly pretty) again, in 1.9.2+ like they used to be?
class Float def pretty_s num = "%.12g" % self num =~ /\..*?(0+)$/ num.sub!($1, '') # might be like 2. at this point num = num[0..-2] if num[-1] == '.' num end end p 1.1-0.9 # >> 0.20000000000000007 p (1.1-0.9).pretty_s # >> "0.2" p 2.0.pretty_s # >> "2"
http://coderrr.wordpress.com/2009/12/22/get-arbitrarily-precise-bigdecimals-in-ruby-for-just-one-extra-character/ os a clever trick to use BigDecimal more easily.
Basically at a certain patch level of 1.9.1, \w was set to no longer match unicode characters, because the core developers were concerned that this was not what people expected from \w.
see this link
With 1.9.0 and 1.9.1, gem uses “gem_prelude” to load files from gems.
It basically (pre) loaded the “lib” paths of each highest numbered gem to your require path.
This sped things up quite a bit for startup time, but introduced a few subtle bugs with rubygems so was set to be used far less in 1.9.2.
In 1.9.2, it does not preload lib paths. Instead, if you ever do a
require 'rubygems' it reverts back to the normal “full” rubygems (adding lib paths “on demand”). In 1.9.1 it also reverts to “full” rubygems, but only if you ever use a gem specific constant or method, like
Gem::Dependency, and it leaves the load path full of the old libs.
In 1.9.1, if you want to avoid using the somewhat buggy gem_prelude, then run your script like
ruby --disable-gems script_name.rb and include the
require 'rubygems' line in your script, or upgrade to 1.9.2
Note: this is not the first ruby faq. Take a step back in history and see the original
Last edited by dlchet,