From: Carlos <angus@...>
Date: 2005-05-28T00:17:54+09:00
Subject: Re: Methods with lots of arguments

[Dido Sevilla <dido.sevilla@gmail.com>, 2005-05-27 08.10 CEST]
> Just went through a bit of refactoring on a bit of Ruby code that I've
> been writing, and have been following some of the guidelines here:
> 
> http://rpa-base.rubyforge.org/wiki/wiki.cgi?GoodAPIDesign
> 
> I've had a lot of methods in the old code that had lots and lots of
> arguments, and many of which had default values, and followed the
> suggestion on naming arguments by passing what is essentially a hash.
> The syntax for this looked a lot like the labeled arguments used in
> OCaml, and it seems like a good way of doing things.  Now only if Ruby
> had actual support for this idiom. As it turns out, I wind up writing
> a lot of methods that look like this:
> 
> def somemethod(args)
>   requiredargs = [ :foo, :bar, :baz ]
>   defaultargs = { :quux => nil, :blargle => nil }
>   requiredargs.each {
>     |arg|
>     unless (args.has_key?(arg))
>       raise ArgumentError.new("missing required argument #{arg.to_s}")
>     end
>   }
>   newargs = defaultargs.merge(args)
>   ...
> end
> 
> Is there at the very least some kind of library out there that can do
> all of this checking and merging automatically? If there is one, I
> think it should be mentioned in the RPA-base link. However, I think
> that this kind of idiom would be better as an official part of Ruby
> syntax.

Well, if you are repeating code, you should put it in a method...

class Hash
	def setup_args! (desc)
		desc[:required] ||= []
		desc[:default] ||= {}
		desc[:required].each do |arg|
			unless self.has_key?(arg)
				raise ArgumentError.new("missing req arg")
			end
		end
		self.replace desc[:default].merge(self)
	end
end

def somemethod (args)
	args.setup_args! (:required => [:foo, :bar, :baz],
			  :default => { :quux => nil, :blarg => 77})
	...
end

(not tested)

HTH