extractor.rb

module Extractor
  MATCH_FAILED = []
  def MATCH_FAILED.length
    -1
  end

  def ===(obj)
    unapply = method(:unapply)
    obj.singleton_class.define_method(:deconstruct) do
      singleton_class.remove_method(:deconstruct)
      unapply.call(obj)
    end
    true
  end
end

class EMail
  class << self
    prepend Extractor

    def unapply(obj)
      parts = obj.to_s.split(/@/)
      if parts.length == 2
        parts
      else
        Extractor::MATCH_FAILED
      end
    end
  end
end

case 'foo-bar@example.com'
in EMail(name, domain)
  p name   #=> "foo-bar"
  p domain #=> "example.com"
end