#     assert [1..1].has_only(1)
	#     assert not [1..10].has_only(1)
	redef fun has_only(item) do return first == item and item == last or is_empty

	redef fun has_only(e)
	do
		mutex.lock
		var r = real_collection.has_only(e)
		mutex.unlock
		return r
	end

	redef fun has_only(an_item) do return item == an_item

	redef fun has_only(item)
	do
		var i = 0
		var l = length
		while i < l do
			if self[i] != item then return false
			i += 1
		end
		return true
	end

	redef fun has_only(k) do return (self.has(k) and self.length == 1) or self.is_empty

	# O(n)
	redef fun has_only(item)
	do
		for i in self.map._items do if i.second != item then return false
		return true
	end

	redef fun has_only(k) do return (self.has(k) and self.length == 1) or self.is_empty

	redef fun has_only(item)
	do
		var c = self.map._first_item
		while c != null do
			if c._value != item then return false
			c = c._next_item
		end
		return true
	end

	redef fun has_only(item)
	do
		var l = length
		if l == 1 then
			return has(item)
		else if l == 0 then
			return true
		else
			return false
		end
	end

	redef fun has_only(e)
	do
		var node = _head
		while node != null do
			if node.item != e then return false
			node = node.next
		end
		return true
	end