gistfile1.rb

class Hash
  alias :old_default :default
  def default(*args)
    ret = old_default(*args)
    ignore_these = [NilClass, TrueClass, FalseClass, Float, Symbol, Rational, Integer]
    case ret
    when *ignore_these: ret
    else ret.dup
    end     
  end
end

# This is to prevent weird behavior such as this:
# h = Hash.new([])
# h['a'].push(1) -> [1]
# h['a'].push(2) -> [1,2]
# h['b'].push(3) -> [1,2,3]
# h['a'] -> [1,2,3]
# h['b'] -> [1,2,3]
#
# Since no assignments are being made, the intuitive behavior would be thus:
# h = Hash.new([])
# h['a'].push(1) -> [1]
# h['a'].push(2) -> [2]
# h['b'].push(3) -> [3]
# h['a'] -> []
# h['b'] -> []