# Return a random element form the collection
	# There must be at least one element in the collection
	#
	# ~~~
	# var x = [1,2,3].rand
	# assert x == 1 or x == 2 or x == 3
	# ~~~
	fun rand: E
	do
		if is_empty then abort
		var rand_index = length.rand

		for e in self do
			if rand_index == 0 then return e
			rand_index -= 1
		end
		abort
	end