# Gets an iterator that progress with a given step.
	#
	# The main usage is in `for` construction.
	#
	# ~~~
	# for i in [10..25].step(10) do assert i == 10 or i == 20
	# ~~~
	#
	# But `step` is usable as any kind of iterator.
	#
	# ~~~
	# assert [10..27].step(5).to_a == [10,15,20,25]
	# ~~~
	#
	# If `step == 1`, then it is equivalent to the default `iterator`.
	#
	# ~~~
	# assert [1..5].step(1).to_a == [1..5].to_a
	# ~~~
	#
	# If `step` is negative, then the iterator will iterate on ranges whose `first` > `last`.
	#
	# ~~~
	# assert [25..12].step(-5).to_a == [25,20,15]
	# ~~~
	#
	# On such ranges, the default `iterator` will be empty
	#
	# ~~~
	# assert [5..1].step(1).to_a.is_empty
	# assert [5..1].iterator.to_a.is_empty
	# assert [5..1].to_a.is_empty
	# assert [5..1].is_empty
	# ~~~
	#
	# Note that on non-empty range, iterating with a negative step will be empty
	#
	# ~~~
	# assert [1..5].step(-1).to_a.is_empty
	# ~~~
	fun step(step: Int): Iterator[E]
	do
		var i
		if step >= 0 then
			i = iterator
		else
			i = new DowntoIteratorRange[E](self)
			step = -step
		end

		if step == 1 then return i
		return i.to_step(step)
	end