def array(method = nil)
      -> (v) do
        if v
          v.split(",").map{|a| cast(a, method) }
        end
      end
    end
def array(method = nil)
      -> (v) do
        if v
          v.split(",").map{|a| cast(a, method) }
        end
      end
    end
optional :accronyms, array(string)
 => ['a', 'b']
 optional :numbers, array(int)
 => [1, 2]
 optional :notype, array
 => ['a', 'b']