indexing
	description: "Unbounded queues implemented as linked lists"
	status: "See notice at end of class"
	names: linked_queue, dispenser, linked_list
	representation: linked
	access: fixed, fifo, membership
	contents: generic
	date: "$Date$"
	revision: "$Revision$"

class interface
	LINKED_QUEUE [G]

create

	make
			-- Create linked queue.

feature -- Initialization

	make
			-- Create linked queue.

feature -- Access

	has (v: like ll_item): BOOLEAN
			-- Does chain include v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty

	item: G
			-- Oldest item
		require -- from ACTIVE
			readable: readable
		ensure then
			last_element_if_not_empty: not is_empty implies (active = last_element)

feature -- Measurement

	count: INTEGER
			-- Number of items
			-- (from LINKED_LIST)

	occurrences (v: like ll_item): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	occurrences (v: like ll_item): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

feature -- Comparison

	is_equal (other: like Current): BOOLEAN
			-- Does other contain the same elements?
			-- (from LIST)
		require -- from ANY
			other_not_void: other /= void
		ensure -- from ANY
			symmetric: Result implies other.is_equal (Current)
			consistent: standard_is_equal (other) implies Result
		ensure then -- from LIST
			indices_unchanged: index = old index and other.index = old other.index
			true_implies_same_size: Result implies count = other.count

feature -- Status report

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

	Extendible: BOOLEAN is True
			-- May new items be added? (Answer: yes.)
			-- (from DYNAMIC_CHAIN)

	Full: BOOLEAN is False
			-- Is structured filled to capacity? (Answer: no.)
			-- (from LINKED_LIST)

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

	is_inserted (v: G): BOOLEAN
			-- Has v been inserted by the most recent insertion?
			-- (By default, the value returned is equivalent to calling
			-- `has (v)'. However, descendants might be able to provide more
			-- efficient implementations.)
			-- (from COLLECTION)

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

	prunable: BOOLEAN
			-- May items be removed? (Answer: yes.)
			-- (from DYNAMIC_CHAIN)

	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)
		require -- from SEQUENCE
			argument_not_void: s /= void
		ensure -- from SEQUENCE
			new_count: count >= old count

	extend (v: G)
			-- Add v as newest item.
			-- Was declared in LINKED_QUEUE as synonym of put and force.
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from BAG
			one_more_occurrence: occurrences (v) = old (occurrences (v)) + 1
		ensure then
			single_item_constraint: (old is_empty) implies (item = v)

	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: G)
			-- Add v as newest item.
			-- Was declared in LINKED_QUEUE as synonym of put and extend.
		require -- from  DISPENSER
			True
		require -- from SEQUENCE
			extendible: extendible
		ensure then -- from SEQUENCE
			new_count: count = old count + 1
			item_inserted: has (v)
		ensure then
			single_item_constraint: (old is_empty) implies (item = v)

	put (v: G)
			-- Add v as newest item.
			-- Was declared in LINKED_QUEUE as synonym of extend and force.
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then
			single_item_constraint: (old is_empty) implies (item = v)

	replace (v: like ll_item)
			-- Replace current item by v.
			-- (from LINKED_LIST)
		require -- from ACTIVE
			writable: writable
		ensure -- from ACTIVE
			item_replaced: item = v

feature -- Removal

	remove
			-- Remove item to the left of cursor position.
			-- Do not move cursor.
			-- (from LINKED_LIST)
		require -- from DYNAMIC_CHAIN
			left_exists: index > 1
		require else -- from DYNAMIC_LIST
			not_before: not before
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count - 1
			new_index: index = old index - 1

	wipe_out
			-- Remove all items.
			-- (from LINKED_LIST)
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			wiped_out: is_empty
		ensure then -- from DYNAMIC_LIST
			is_before: before

feature -- Conversion

	linear_representation: ARRAYED_LIST [G]
			-- Representation as a linear structure
			-- (order is same as original order of insertion)

feature -- Duplication

	copy (other: like Current)
			-- Update current object using fields of object attached
			-- to other, so as to yield equal objects.
			-- (from LINKED_LIST)
		require -- from ANY
			other_not_void: other /= void
			type_identity: same_type (other)
		ensure -- from ANY
			is_equal: is_equal (other)

	duplicate (n: INTEGER): like Current
			-- New queue containing the n oldest items in current queue.
			-- If n is greater than count, identical to current queue.
		require -- from CHAIN
			not_off_unless_after: off implies after
			valid_subchain: n >= 0

invariant

	is_always_after: not is_empty implies after
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from DISPENSER
	readable_definition: readable = not is_empty
	writable_definition: writable = not is_empty
		-- from ACTIVE
	writable_constraint: writable implies readable
	empty_constraint: is_empty implies (not readable) and (not writable)
		-- from FINITE
	empty_definition: is_empty = (count = 0)
	non_negative_count: count >= 0
		-- from LINKED_LIST
	prunable: prunable
	empty_constraint: is_empty implies ((first_element = void) and (active = void))
	not_void_unless_empty: (active = void) implies is_empty
	before_constraint: before implies (active = first_element)
	after_constraint: after implies (active = last_element)
		-- from LIST
	before_definition: before = (index = 0)
	after_definition: after = (index = count + 1)
		-- from CHAIN
	non_negative_index: index >= 0
	index_small_enough: index <= count + 1
	off_definition: off = ((index = 0) or (index = count + 1))
	isfirst_definition: isfirst = ((not is_empty) and (index = 1))
	islast_definition: islast = ((not is_empty) and (index = count))
	item_corresponds_to_index: (not off) implies (ll_item = i_th (index))
	index_set_has_same_count: index_set.count = count
		-- from INDEXABLE
	index_set_not_void: index_set /= void
		-- from BILINEAR
	not_both: not (after and before)
	before_constraint: before implies off
		-- from LINEAR
	after_constraint: after implies off
		-- from TRAVERSABLE
	empty_constraint: is_empty implies off
		-- from DYNAMIC_CHAIN
	extendible: extendible

indexing
	library: "[
			EiffelBase: Library of reusable components for Eiffel.
	]"
	status: "[
			Copyright 1986-2001 Interactive Software Engineering (ISE).
			For ISE customers the original versions are an ISE product
			covered by the ISE Eiffel license and support agreements.
	]"
	license: "[
			EiffelBase may now be used by anyone as FREE SOFTWARE to
			develop any product, public-domain or commercial, without
			payment to ISE, under the terms of the ISE Free Eiffel Library
			License (IFELL) at http://eiffel.com/products/base/license.html.
	]"
	source: "[
			Interactive Software Engineering Inc.
			ISE Building
			360 Storke Road, Goleta, CA 93117 USA
			Telephone 805-685-1006, Fax 805-685-6869
			Electronic mail <info@eiffel.com>
			Customer support http://support.eiffel.com
	]"
	info: "[
			For latest info see award-winning pages: http://eiffel.com
	]"

end -- class LINKED_QUEUE