Anagram discoverer in Ruby

anagram.rb

require 'set'

class Anagram
  DefaultWordlist = (File.open '/usr/share/dict/words' rescue [])
    .inject(Set.new) { |s, word| s << word.downcase.chomp }

  def initialize(wordlist = DefaultWordlist)
    @wordlist_signed = wordlist
      .inject(Hash.new { [] }) { |h, word| h[sign(word)] <<= word; h }
  end

  def solve(word)
    @wordlist_signed[sign(word)] - [word]
  end

  private

  def sign(word)
    word.downcase.chars.sort.join
  end
end