class Array

def shift_with_optional_argument(n = Backports::Undefined) 

def shift_with_optional_argument(n = Backports::Undefined)
  return shift_without_optional_argument if n == Backports::Undefined
  n = Backports.coerce_to_int(n)
  raise ArgumentError, "negative array size" if n < 0
  slice!(0, n)
end