# Returns a rail-fence cipher from `self` with `depth` rails
	#
	# Rail works by drawing a zig-zag pattern on `depth` rails.
	#
	# Say we have "fuckingbehemoth".railfence(4)
	#
	# This happens in-memory:
	#
	# ~~~raw
	# f.....g.....o..
	# .u...n.b...m.t.
	# ..c.i...e.e...h
	# ...k.....h.....
	# ~~~
	#
	# Therefore, yielding the ciphertext : "fgounbmtcieehkh"
	#
	#     assert "fuckingbehemoth".railfence(4) == "fgounbmtcieehkh"
	fun railfence(depth: Int): Text do
		var lines = new Array[FlatBuffer].with_capacity(depth)
		var up = false
		for i in [0..depth[ do
			lines[i] = new FlatBuffer.with_capacity(length)
		end
		var curr_depth = 0
		for i in chars do
			for j in [0..depth[ do
				if j == curr_depth then
					lines[j].add i
				else
					lines[j].add '.'
				end
			end
			if up then
				curr_depth -= 1
			else
				curr_depth += 1
			end
			if curr_depth == 0 then
				up = false
			end
			if curr_depth == (depth - 1) then
				up = true
			end
		end
		var r = new FlatBuffer.with_capacity(length)
		for i in lines do
			r.append i.to_s.replace(".", "")
		end
		return r.to_s
	end