[] ~/projects/jruby $ cat blah.rb
class Splash                                                                                                                                          
  def to_proc                                                                                                                                         
    proc do |*a|                                                                                                                                         
      a                                                                                                                                             
    end                                                                                                                                               
  end                                                                                                                                                 
end                                                                                                                                 

p [1,2].map(&Splash.new)        # --> [[1],[2]] correct
p  [[1,2]].map(&Splash.new)    # --> [[1,2]] one set of brackets missing                                                                                                            
p ->(*a){ a }.([[1,2]])    

[] ~/projects/jruby $ jruby blah.rb
[[1], [2]]
[[[1, 2]]]
[[[1, 2]]]