Required named parameters snippet, gleaned from http://stackoverflow.com/questions/13250447/can-i-have-required-named-parameters-in-ruby-2-x

required.rb

def required(arg=nil)
  method = caller_locations(1,1)[0].label
  raise ArgumentError.new("required parameter #{arg.to_sym.inspect + ' ' if arg}not passed to method #{method}")
end

def say(greeting: required('greeting'))
  puts greeting
end

def say2(greeting: required)
  puts greeting
end

def say3(greeting: required(:greeting))
  puts greeting
end

# say
# test.rb:3:in `required': required parameter :greeting not passed to method say (ArgumentError)
#        from test.rb:6:in `say'
#        from test.rb:18:in `<main>'

# say2
# test.rb:3:in `required': required parameter not passed to method say2 (ArgumentError)
#        from test.rb:10:in `say2'
#        from test.rb:23:in `<main>'

# say3
#test.rb:3:in `required': required parameter :greeting not passed to method say3 (ArgumentError)
#        from test.rb:14:in `say3'
#        from test.rb:28:in `<main>'

# calling it like say('greeting') results in ArgumentError

say greeting: 'greeting'