From: Roger Pack <rogerpack2005@...>
Date: 2009-12-16T00:30:34+09:00
Subject: Re: Introspecting Method Arguments with Method.arity


> Documentation reveals that when a method has optional arguments, the
> arity is -n - 1 where n is the number of required arguments (which
> seems a little arbitrary, is there a historical reason for this?).

I was reading something about this the other day in README.EXT -- its 
description of rb_define_method I think.

Basically "-1 and -2 are magic numbers" denoting the type of argument 
your C method expects (an array or not).  Something like that.

> Is there a way to return the number of required arguments, the number
> of optional arguments and whether or not a splat is present for a
> method?

arguments (or rdp-arguments gem) gems might be useful for you.


[this snippet'll need to be in a file for 1.9]
require 'rubygems'
require 'arguments'
class A
 def go a, b = 3, *args
 end
end
puts Arguments.names A, :go, false
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