# Comparable array for comparable elements.
#
# For two arrays, if one is a prefix, then it is lower.
#
# ~~~
# var a12 = new ArrayCmp[nullable Int].with_items(1,2)
# var a123 = new ArrayCmp[nullable Int].with_items(1,2,3)
# assert a12 < a123
# ~~~
#
# Otherwise, the first element just after the longest
# common prefix gives the order between the two arrays.
#
# ~~~
# var a124 = new ArrayCmp[nullable Int].with_items(1,2,4)
# var a13 = new ArrayCmp[nullable Int].with_items(1,3)
# assert a12  < a123
# assert a123 < a13
# ~~~
#
# Obviously, two equal arrays are equal.
#
# ~~~
# var b12 = new ArrayCmp[nullable Int].with_items(1,2)
# assert (a12 <=> b12) == 0
# ~~~
#
# `null` is considered lower than any other elements.
# But is still greater than no element.
#
# ~~~
# var a12n = new ArrayCmp[nullable Int].with_items(1,2,null)
# assert a12n < a123
# assert a12  < a12n
# ~~~
class ArrayCmp[E: nullable Comparable]
	super Array[E]
	super Comparable
	redef type OTHER: ArrayCmp[E] is fixed

	redef fun <(o) do return (self <=> o) < 0

	redef fun <=>(o)
	do
		var i = 0
		var l = length
		if l == 0 then return 0
		var it = _items.as(not null)
		var oit = o._items.as(not null)
		var ol = o.length
		var len
		if l < ol then len = l else len = ol
		while i < len do
			var a = it[i]
			var b = oit[i]
			if a != null then
				if b == null then return 1
				var d = a <=> b
				if d != 0 then return d
			else
				if b != null then return -1
			end
			i += 1
		end
		return l <=> ol
	end
end