indexing
	description: "Priority queues implemented as heaps"
	names: sorted_priority_queue, dispenser, heap
	representation: heap
	access: fixed, membership
	contents: generic

class interface
	HEAP_PRIORITY_QUEUE [G -> COMPARABLE]

create 

	make (n: INTEGER)
			-- Allocate heap space.

feature -- Initialization

	make (n: INTEGER)
			-- Allocate heap space.

	setup (other: like Current)
			-- Perform actions on a freshly created object so that
			-- the contents of other can be safely copied onto it.
			-- (from ARRAY)
		ensure -- from GENERAL
			consistent (other)
	
feature -- Access

	has (v: G): BOOLEAN
			-- Does v appear in array?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from ARRAY)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not empty

	item: G
			-- Entry at top of heap.
		require -- from ACTIVE
			readable: readable
	
feature -- Measurement

	count: INTEGER

	occurrences (v: G): INTEGER
			-- Number of times v appears in structure
			-- (from ARRAY)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0
	
feature -- Comparison

	is_equal (other: like Current): BOOLEAN
			-- Is array made of the same items as other?
			-- (from ARRAY)
		require -- from GENERAL
			other_not_void: other /= void
		ensure -- from GENERAL
			symmetric: Result implies other.is_equal (Current);
			consistent: standard_is_equal (other) implies Result
	
feature -- Status report

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

	consistent (other: like Current): BOOLEAN
			-- Is object in a consistent state so that other
			-- may be copied onto it? (Default answer: yes).
			-- (from ARRAY)

	empty: BOOLEAN
			-- Is structure empty?
			-- (from FINITE)

	extendible: BOOLEAN
			-- May items be added?

	full: BOOLEAN
			-- Is structure filled to capacity?

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

	Prunable: BOOLEAN is true
			-- May items be removed? (Answer: yes.)

	readable: BOOLEAN
			-- Is there a current item that may be read?
			-- (from DISPENSER)

	writable: BOOLEAN
			-- Is there a current item that may be modified?
			-- (from DISPENSER)
	
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 -- Element change

	append (s: SEQUENCE [G])
			-- Append a copy of s.
			-- (Synonym for fill)
			-- (from DISPENSER)

	fill (other: CONTAINER [G])
			-- Fill with as many items of other as possible.
			-- The representations of other and current structure
			-- need not be the same.
			-- (from COLLECTION)
		require -- from COLLECTION
			other_not_void: other /= void;
			extendible

	force (v: like item)
			-- Insert item v at its proper position.
			-- Was declared in HEAP_PRIORITY_QUEUE as synonym of force and put.

	put (v: like item)
			-- Insert item v at its proper position.
			-- Was declared in HEAP_PRIORITY_QUEUE as synonym of force and put.
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: has (v)
	
feature -- Removal

	prune_all (v: G)
			-- Remove all occurrences of v.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from COLLECTION)
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			no_more_occurrences: not has (v)

	remove
			-- Remove item of highest value.
		require -- from ACTIVE
			prunable: prunable;
			writable: writable

	wipe_out
			-- Make array empty.
			-- (from ARRAY)
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			wiped_out: empty
	
feature -- Conversion

	linear_representation: ARRAYED_LIST [G]
			-- Representation as a linear structure
			-- (Sorted according to decreasing priority)
	
feature -- Duplication

	copy (other: like Current)
			-- Reinitialize by copying all the items of other.
			-- (This is also used by clone.)
			-- (from ARRAY)
		require -- ARRAY
			precursor: True
		require -- from GENERAL
			other_not_void: other /= void;
			type_identity: same_type (other)
ensure -- from GENERAL
			is_equal: is_equal (other)

	duplicate (n: INTEGER): like Current
			-- New priority queue containing the n greatest items
	
feature -- Inapplicable

	extend (v: G)
			-- Add v to structure.
			-- (Precondition is false.)
			-- (from ARRAY)
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: has (v)
		ensure then -- from BAG
			one_more_occurrence: occurrences (v) = old (occurrences (v)) + 1

	prune (v: G)
			-- Remove first occurrence of v if any.
			-- (Precondition is false.)
			-- (from ARRAY)
		require -- from COLLECTION
			prunable: prunable
	
invariant

		-- from GENERAL
	reflexive_equality: standard_is_equal (Current);
	reflexive_conformance: conforms_to (Current);
		-- from DISPENSER
	readable_definition: readable = not empty;
	writable_definition: writable = not empty;
		-- from ACTIVE
	writable_constraint: writable implies readable;
	empty_constraint: empty implies (not readable) and (not writable);
		-- from FINITE
	empty_definition: empty = (count = 0);
	non_negative_count: count >= 0;
		-- from ARRAY
non_negative_count: count >= 0;

end -- class HEAP_PRIORITY_QUEUE