Are mandatory keyword args a thing? I find myself wanting to do this a lot. UPDATE: answer is yes, see https://gist.github.com/JacobNinja/a38d0f4b02759c910dc3

mandatory_keyword_args.rb

def mandatory
  required    = method(caller.first[/(?<=`).*(?=')/]         # => "crazy_arglist!"
                      )                                      # => #<Method: Object#crazy_arglist!>
                      .parameters                            # => [[:req, :a], [:opt, :b], [:rest, :c], [:key, :d], [:key, :e], [:keyrest, :f], [:block, :g]]
                      .select { |type, name| type == :key }  # => [[:key, :d], [:key, :e]]
                      .map    { |type, name| name }          # => [:d, :e]
  raise ArgumentError, "Must provide #{required.join ", "}"  # ~> ArgumentError: Must provide d, e
end

def crazy_arglist!(a, b=1, *c, d: mandatory, e: mandatory, **f, &g)
  "line #{caller.first.split(":")[1]}"                               # => "line 16"
end


# works when you provide the mandatory args
crazy_arglist! nil, d: nil, e: nil  # => "line 16"

# blows up when you don't, but is kind enough to tell you what you omitted, at least
crazy_arglist! nil

# ~> ArgumentError
# ~> Must provide d, e
# ~>
# ~> /var/folders/7g/mbft22555w3_2nqs_h1kbglw0000gn/T/seeing_is_believing_temp_dir20140502-17238-1bfctnw/program.rb:7:in `mandatory'
# ~> /var/folders/7g/mbft22555w3_2nqs_h1kbglw0000gn/T/seeing_is_believing_temp_dir20140502-17238-1bfctnw/program.rb:10:in `crazy_arglist!'
# ~> /var/folders/7g/mbft22555w3_2nqs_h1kbglw0000gn/T/seeing_is_believing_temp_dir20140502-17238-1bfctnw/program.rb:19:in `<main>'