gistfile1.rb

require 'active_support/inflector'
require 'benchmark'

# QUICK HACK
class RuleSet
  def initialize
    @rules  = []
    @regexp = nil
  end

  def prepend_rule(pattern, replacement)
    @rules.unshift([pattern, replacement])
    patterns = @rules.each_with_index.map {|rule, i| build_regexp(rule.first, i)}
    @regexp = Regexp.union(*patterns)
  end

  def build_regexp(pattern, i)
    pattern = Regexp.quote(pattern) if pattern.is_a?(String)
    /(?<_#{i}>#{pattern})/
  end

  def apply(word)
    word = word.to_s.dup
    if md = @regexp.match(word)
      name = md.names.detect {|n| md[n]}
      index = name[/\d+/, 0].to_i
      word.gsub!(@rules[index][0], @rules[index][1])
    end
    word
  end
end

rs = RuleSet.new
ActiveSupport::Inflector::Inflections.instance.plurals.each do |pattern, replacement|
  rs.prepend_rule(pattern, replacement)
end

words = File.readlines('/usr/share/dict/words').map(&:chomp)

Benchmark.bmbm do |x|
  x.report('AS') { words.each {|word| ActiveSupport::Inflector.pluralize(word) }}
  x.report('RS') { words.each {|word| rs.apply(word) }}
end

__END__
Rehearsal --------------------------------------
AS  78.620000   0.940000  79.560000 ( 82.188521)
RS  11.630000   0.100000  11.730000 ( 11.876435)
---------------------------- total: 91.290000sec

         user     system      total        real
AS  80.500000   0.890000  81.390000 ( 83.407733)
RS  11.520000   0.100000  11.620000 ( 11.855246)