# Removes the whitespaces at the end of self
	#
	# ~~~
	# assert " \n\thello \n\t".r_trim == " \n\thello"
	# ~~~
	#
	# `Char::is_whitespace` determines what is a whitespace.
	fun r_trim: SELFTYPE
	do
		var iter = self.chars.reverse_iterator
		while iter.is_ok do
			if not iter.item.is_whitespace then break
			iter.next
		end
		if iter.index < 0 then return self.empty
		return self.substring(0, iter.index + 1)
	end