forward1.rb

def bar(*a)
  p a
end

bar(1, a: 1)

def foo(a, ...)
  bar(...)
end

foo(1, 2, 3, **{})

gistfile1.txt

system ~/work/jruby master 2542% mri31 ../snippets/forward1.rb 
[1, {:a=>1}]
[2, 3]
system ~/work/jruby master 2543% mri30 ../snippets/forward1.rb 
[1, {:a=>1}]
[2, 3]
system ~/work/jruby master 2544% jruby ../snippets/forward1.rb 
[1, {:a=>1}]
[2, 3, {}]
system ~/work/jruby master 2545% jruby --dev ../snippets/forward1.rb 
[1, {:a=>1}]
[2, 3]