Ruby 2.0 keyword arguments

keyword.rb

def foo(str: "foo", num: 123456)
  [str, num]
end

p foo(str: 'buz', num: 9) #=> ['buz', 9]
p foo(str: 'bar') # => ['bar', 123456]
p foo(num: 123) # => ['foo', 123]
p foo # => ['foo', 123456]
p foo(bar: 'buz') # => ArgumentError