parameters.rb

class Foo
  def bar(arg)
  end
  def baz(arg=nil)
  end
  def frobnicate(*arg)
  end
  def blocky(&block)
  end
  def hairy(first,second=2,*middle,last)
  end
end

foo = Foo.new
(foo.methods - Object.new.methods).each do |name|
  m = foo.method(name)
  p [name, m.parameters]
end

# => [:bar, [[:req, :arg]]]
# => [:baz, [[:opt, :arg]]]
# => [:frobnicate, [[:rest, :arg]]]
# => [:blocky, [[:block, :block]]]


procy = proc {|first,second=2,*middle,last| }
p procy.parameters

# => [[:opt, :first], [:opt, :second], [:rest, :middle], [:opt, :last]]