# Associative arrays that internally uses couples to represent each (key, value) pairs.
# This is an helper class that some specific implementation of Map may implements.
interface CoupleMap[K, V]
	super Map[K, V]

	# Return the couple of the corresponding key
	# Return null if the key is no associated element
	protected fun couple_at(key: nullable Object): nullable Couple[K, V] is abstract

	# Return a new iteralot on all couples
	# Used to provide `iterator` and others
	protected fun couple_iterator: Iterator[Couple[K,V]] is abstract

	redef fun iterator do return new CoupleMapIterator[K,V](couple_iterator)

	redef fun [](key)
	do
		var c = couple_at(key)
		if c == null then
			return provide_default_value(key)
		else
			return c.second
		end
	end

	redef fun has_key(key) do return couple_at(key) != null
end