class Array

def sample(n = Backports::Undefined, options = Backports::Undefined)
  if options == Backports::Undefined && n.respond_to?(:to_hash)
    n, options = options, n
  end
  rng = Backports.coerce_to_option(options, :random) unless options == Backports::Undefined
  generator = if rng.respond_to? :rand
    Proc.new do |nb|
      r = Backports::coerce_to_int(rng.rand(nb))
      raise RangeError, "random generator returned #{r} which is not in 0...#{nb}" if r < 0 || r >= nb
      r
    end
  else
    Kernel.method(:rand)
  end
  return self[generator.call(size)] if n == Backports::Undefined
  n = Backports.coerce_to_int(n)
  raise ArgumentError, "negative array size" if n < 0
  n = size if n > size
  result = Array.new(self)
  n.times do |i|
    r = i + generator.call(size - i)
    result[i], result[r] = result[r], result[i]
  end
  result[n..size] = []
  result
end