Ruby 2.1

Named arguments with defaults

# length is required
def pad(num, length:, char: "0")
  num.to_s.rjust(length, char)
end

pad(42, length: 6)   #=> "000042"
pad(42)              #=> #<ArgumentError: missing keyword: length>

Module.prepend

prepend(Module.new do
  define_method ...
end)

References

• http://globaldev.co.uk/2013/03/ruby-2-0-0-in-detail
• http://globaldev.co.uk/2014/05/ruby-2-1-in-detail