indexing
	description:
		"Containers that have a current position"

	status:	"See note at end of class"
	date: "$Date$"
	revision: "$Revision$"

deferred class ACTIVE_CONTAINER [G] inherit

	BASIC_CONTAINER [G]

feature -- Access

	item: G is
			-- Current item
		require
			not_empty: not is_empty
		deferred
		ensure
			non_void_result: Result /= Void
		end

	i_th (i: INTEGER): G is
			-- `i'-th item
		require
			not_empty: not is_empty
			valid_index: valid_index (i)
		deferred
		ensure
			index_unchanged: index = old index
		end

	index: INTEGER is
			-- Current index
		deferred
		end
	
feature -- Status setting

	go_i_th (i: INTEGER) is
			-- Go to `i'-th position.
		require
			not_empty: not is_empty
			valid_index: valid_index (i)
		deferred
		ensure
			index_set: index = i
		end

invariant

	index_in_range: not is_empty implies valid_index (index)

end -- class ACTIVE_CONTAINER

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