indexing
	description: "Data structures whose items may be compared according to a total order relation"
	names: comparable_struct
	access: min, max
	contents: generic

deferred class interface
	COMPARABLE_STRUCT [G -> COMPARABLE]

feature -- Access

	has (v: like item): BOOLEAN
			-- Does structure include an occurrence of v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not empty

	index_of (v: like item; i: INTEGER): INTEGER
			-- Index of i-th occurrence of v.
			-- 0 if none.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		require -- from LINEAR
			positive_occurrences: i > 0
		ensure -- from LINEAR
			non_negative_result: Result >= 0

	item: G
			-- Item at current position
			-- (from TRAVERSABLE)
		require -- from TRAVERSABLE
			not_off: not off
		require -- from TRAVERSABLE
			not_off: not off

	occurrences (v: G): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)

	off: BOOLEAN
			-- Is there no current item?
			-- (from BILINEAR)
	
feature -- Measurement

	max: like item
			-- Maximum item
		require
			min_max_available

	min: like item
			-- Minimum item
		require
			min_max_available

	min_max_available: BOOLEAN
			-- Can min and max be computed?
		ensure
			Result implies not empty
	
feature -- Status report

	after: BOOLEAN
			-- Is there no valid position to the right of current one?
			-- (from LINEAR)

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)

	empty: BOOLEAN
			-- Is there no element?
			-- (from CONTAINER)

	exhausted: BOOLEAN
			-- Has structure been completely explored?
			-- (from LINEAR)
		ensure -- from LINEAR
			exhausted_when_off: off implies Result

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)
	
feature -- Status setting

	compare_objects
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			object_comparison

	compare_references
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			reference_comparison: not object_comparison
	
feature -- Cursor movement

	back
			-- Move to previous position.
			-- (from BILINEAR)
		require -- from BILINEAR
			not_before: not before

	before: BOOLEAN
			-- Is there no valid position to the left of current one?
			-- (from BILINEAR)

	finish
			-- Move to last position.
			-- (from LINEAR)

	forth
			-- Move to next position; if no next position,
			-- ensure that exhausted will be true.
			-- (from LINEAR)
		require -- from LINEAR
			not_after: not after
		require -- from LINEAR
			not_after: not after

	search (v: like item)
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- If structure does not include v ensure that
			-- exhausted will be true.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from BILINEAR)
		ensure -- from LINEAR
			object_found: (not exhausted and object_comparison) implies equal (v, item);
			item_found: (not exhausted and not object_comparison) implies v = item

	start
			-- Move to first position if any.
			-- (from TRAVERSABLE)
	
feature -- Conversion

	linear_representation: LINEAR [G]
			-- Representation as a linear structure
			-- (from LINEAR)
	
invariant

		-- from GENERAL
	reflexive_equality: standard_is_equal (Current);
	reflexive_conformance: conforms_to (Current);
	empty_constraint: min_max_available implies not empty;
		-- from BILINEAR
	not_both: not (after and before);
	empty_property: empty implies (after or before);
	before_constraint: before implies off;
		-- from LINEAR
	after_constraint: after implies off;
		-- from TRAVERSABLE
	empty_constraint: empty implies off;

end -- class COMPARABLE_STRUCT