Using a mixin to extend the object and use it's eigenclass

string_introspection_mixin.rb

module MyString
  def consonants
    self.gsub /[aeiuo0-9]/i, ''
  end

  def vowels
    self.gsub /[^aieou]/i, ''
  end

  def capitols
    self.gsub /[^A-Z]/, ''
  end

  def lowercase
    self.gsub /[^a-z]/, ''
  end

  def numbers
    self.gsub /[^0-9]/, ''
  end
end

puts str = "f2fp2LOCBVXBn2ifcgpy".extend(MyString)

%w{consonants vowels capitols lowercase numbers}.each {|m| puts "#{m}: #{str.send m}"}