indexing
	description: "Hash tables, used to store items identified by hashable keys"
	instructions: "[
		Several procedures are provided for inserting an item
		with a given key.
		
		Here is how to choose between them:
		
			- Use `put' if you want to do an insertion only if
			  there was no item with the given key, doing nothing
			  otherwise. (You can find out on return if there was one,
			  and what it was.)
		
			- Use `force' if you always want to insert the item;
			  if there was one for the given key it will be removed,
			  (and you can find out on return what it was).
		
			- Use `extend' if you are sure there is no item with
			  the given key, enabling faster insertion (but
			  unpredictable behavior if this assumption is not true).
		
			- Use `replace' if you want to replace an already present
			  item with the given key, and do nothing if there is none.
		
		In addition you can use `replace_key' to change the key of an
		already present item, identified by its previous key, or
		do nothing if there is nothing for that previous key.
		You can find out on return.
	]"
	instructions: "[
		To find out whether a key appears in the table, use `has'.
		To find out the item, if any, associated with a certain key,
		use `item'.
		
		Both of these routines perform a search. If you need
		both pieces of information (does a key appear? And, if so,
		what is the associated item?), you can avoid performing
		two redundant traversals by using instead the combination
		of `search', `found' and `found_item' as follows: 
		
			your_table.search (your_key)
			if your_table.found then
				what_you_where_looking_for := your_table.found_item
				... Do whatever is needed to `what_you_were_looking_for' ... 
			else
				... No item was present for `your_key' ...
			end
	]"
	compatibility: "[
		This version of the class accepts any value of type H as key.
		Previous versions did not accept the default value as a key;
		this restriction no longer applies. Most clients of the old version
		should work correctly with this one; a client that explicitly relied
		on the default value not being hashable should use the old version
		available in the EiffelBase 3.3 compatibility cluster.
		
		Also, `force' now sets either `found' or `not_found'.
		(Previously it would always set `inserted'.)
	]"
	storable_compatibility: "[
		Persistent instances of the old version of this class will not be
		 retrievable with the present version.
	]"
	warning: "[
		Modifying an object used as a key by an item present in a table will
		cause incorrect behavior. If you will be modifying key objects,
		pass a clone, not the object itself, as key argument to
		`put' and `replace_key'.
	]"
	status: "See notice at end of class"
	date: "$Date$"
	revision: "$Revision$"

class interface
	HASH_TABLE [G, H -> HASHABLE]

create

	make (n: INTEGER)
			-- Allocate hash table for at least n items.
			-- The table will be resized automatically
			-- if more than n items are inserted.
		ensure
			breathing_space: n * 100 < capacity * initial_occupation
			minimum_space: minimum_capacity * 100 < capacity * initial_occupation
			more_than_minimum: capacity >= minimum_capacity
			no_status: not special_status

feature -- Initialization

	accommodate (n: INTEGER)
			-- Reallocate table with enough space for n items;
			-- keep all current items.
		require
			n >= 0
		ensure
			count_not_changed: count = old count
			slot_count_same_as_count: used_slot_count = count
			breathing_space: count * 100 < capacity * initial_occupation

	make (n: INTEGER)
			-- Allocate hash table for at least n items.
			-- The table will be resized automatically
			-- if more than n items are inserted.
		ensure
			breathing_space: n * 100 < capacity * initial_occupation
			minimum_space: minimum_capacity * 100 < capacity * initial_occupation
			more_than_minimum: capacity >= minimum_capacity
			no_status: not special_status

feature -- Access

	current_keys: ARRAY [H]
			-- New array containing actually used keys, from 1 to count
		ensure
			good_count: Result.count = count

	cursor: CURSOR
			-- Current cursor position
		ensure
			cursor_not_void: Result /= void

	found_item: G
			-- Item, if any, yielded by last search operation

	has (key: H): BOOLEAN
			-- Is there an item in the table with key key?
		ensure then
			default_case: (key = computed_default_key) implies (Result = has_default)

	has_item (v: G): BOOLEAN
			-- Does structure include v?
			-- (Reference or object equality,
			-- based on object_comparison.)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty

	item (key: H): G
			-- Item associated with key, if present
			-- otherwise default value of type G
			-- Was declared in HASH_TABLE as synonym of @.
		require -- from TABLE
			valid_key: valid_key (k)
		ensure then
			default_value_if_not_present: (not (has (key))) implies (Result = computed_default_value)

	item_for_iteration: G
			-- Element at current iteration position
		require
			not_off: not off

	key_for_iteration: H
			-- Key at current iteration position
		require
			not_off: not off
		ensure
			at_iteration_position: Result = key_at (iteration_position)

	infix "@" (key: H): G
			-- Item associated with key, if present
			-- otherwise default value of type G
			-- Was declared in HASH_TABLE as synonym of item.
		require -- from TABLE
			valid_key: valid_key (k)
		ensure then
			default_value_if_not_present: (not (has (key))) implies (Result = computed_default_value)

feature -- Measurement

	capacity: INTEGER
			-- Number of items that may be stored.

	count: INTEGER
			-- Number of items in table

	occurrences (v: G): INTEGER
			-- Number of table items equal to v.
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

feature -- Comparison

	is_equal (other: like Current): BOOLEAN
			-- Does table contain the same information as other?
		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

feature -- Status report

	after: BOOLEAN
			-- Is cursor past last item?
			-- Was declared in HASH_TABLE as synonym of off.
		ensure
			definition: Result = ((not has_default and (iteration_position >= capacity)) or (has_default and (iteration_position = (capacity + 1))))

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

	conflict: BOOLEAN
			-- Did last operation cause a conflict?

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

	found: BOOLEAN
			-- Did last operation find the item sought?

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

	inserted: BOOLEAN
			-- Did last operation insert an item?

	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)

	not_found: BOOLEAN
			-- Did last operation fail to find the item sought?

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

	off: BOOLEAN
			-- Is cursor past last item?
			-- Was declared in HASH_TABLE as synonym of after.
		ensure
			definition: Result = ((not has_default and (iteration_position >= capacity)) or (has_default and (iteration_position = (capacity + 1))))

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

	removed: BOOLEAN
			-- Did last operation remove an item?

	replaced: BOOLEAN
			-- Did last operation replace an item?

	valid_cursor (c: CURSOR): BOOLEAN
			-- Can cursor be moved to position c?
		require
			c_not_void: c /= void

	valid_key (k: H): BOOLEAN
			-- Is k a valid key?
			-- (Answer: always yes for hash tables in this version)
		ensure then
			Result

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

	forth
			-- Advance cursor to next occupied position,
			-- or off if no such position remains.
		require
			not_off: not off

	go_to (c: CURSOR)
			-- Move to position c.
		require
			c_not_void: c /= void
			valid_cursor: valid_cursor (c)

	search (key: H)
			-- Search for item of key key.
			-- If found, set found to true, and set
			-- found_item to item associated with key.
		ensure
			found_or_not_found: found or not_found
			item_if_found: found implies (found_item = content.item (position))

	start
			-- Bring cursor to first position.

feature -- Element change

	extend (new: G; key: H)
			-- Assuming there is no item of key key,
			-- insert new with key.
			-- Set inserted.
			--
			-- To choose between various insert/replace procedures,
			-- see instructions in the Indexing clause.
		require
			not_present: not has (key)
		ensure
			inserted: inserted
			insertion_done: item (key) = new
			one_more: count = old count + 1
			same_slot_count_or_one_more_unless_reallocated: (used_slot_count = old used_slot_count) or (used_slot_count = old used_slot_count + 1) or (used_slot_count = count)
			default_property: has_default = ((key = computed_default_key) or (old has_default))

	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 (new: G; key: H)
			-- Update table so that new will be the item associated
			-- with key.
			-- If there was an item for that key, set found
			-- and set found_item to that item.
			-- If there was none, set not_found and set
			-- found_item to the default value.
			--
			-- To choose between various insert/replace procedures,
			-- see instructions in the Indexing clause.
		require else
			True
		ensure then
			insertion_done: item (key) = new
			now_present: has (key)
			found_or_not_found: found or not_found
			not_found_if_was_not_present: not_found = not (old has (key))
			same_count_or_one_more: (count = old count) or (count = old count + 1)
			same_slot_count_or_one_more_unless_reallocated: (used_slot_count = old used_slot_count) or (used_slot_count = old used_slot_count + 1) or (used_slot_count = count)
			found_item_is_old_item: found implies (found_item = old (item (key)))
			default_value_if_not_found: not_found implies (found_item = computed_default_value)
			default_property: has_default = ((key = computed_default_key) or ((key /= computed_default_key) and (old has_default)))

	put (new: G; key: H)
			-- Insert new with key if there is no other item
			-- associated with the same key.
			-- Set inserted if and only if an insertion has
			-- been made (i.e. key was not present).
			-- If so, set position to the insertion position.
			-- If not, set conflict.
			-- In either case, set found_item to the item
			-- now associated with key (previous item if
			-- there was one, new otherwise).
			--
			-- To choose between various insert/replace procedures,
			-- see instructions in the Indexing clause.
		require -- from TABLE
			valid_key: valid_key (k)
		ensure then
			conflict_or_inserted: conflict or inserted
			insertion_done: inserted implies item (key) = new
			now_present: inserted implies has (key)
			one_more_if_inserted: inserted implies (count = old count + 1)
			one_more_slot_if_inserted_unless_reallocated: inserted implies ((used_slot_count = old used_slot_count + 1) or (used_slot_count = count))
			unchanged_if_conflict: conflict implies (count = old count)
			same_item_if_conflict: conflict implies (item (key) = old (item (key)))
			slot_count_unchanged_if_conflict: conflict implies (used_slot_count = old used_slot_count)
			found_item_associated_with_key: found_item = item (key)
			new_item_if_inserted: inserted implies (found_item = new)
			old_item_if_conflict: conflict implies (found_item = old (item (key)))
			default_property: has_default = ((inserted and (key = computed_default_key)) or ((conflict or (key /= computed_default_key)) and (old has_default)))

	replace (new: G; key: H)
			-- Replace item at key, if present,
			-- with new; do not change associated key.
			-- Set replaced if and only if a replacement has been made
			-- (i.e. key was present); otherwise set not_found.
			-- Set found_item to the item previously associated
			-- with key (default value if there was none).
			--
			-- To choose between various insert/replace procedures,
			-- see instructions in the Indexing clause.
		ensure
			replaced_or_not_found: replaced or not_found
			insertion_done: replaced implies item (key) = new
			no_change_if_not_found: not_found implies item (key) = old (item (key))
			found_item_is_old_item: found_item = old (item (key))

	replace_key (new_key: H; old_key: H)
			-- If there is an item of key old_key and no item of key
			-- new_key, replace the former's key by new_key,
			-- set replaced, and set found_item to the item
			-- previously associated with old_key.
			-- Otherwise set not_found or conflict respectively.
			-- If conflict, set found_item to the item previously
			-- associated with new_key.
			--
			-- To choose between various insert/replace procedures,
			-- see instructions in the Indexing clause.
		ensure
			same_count: count = old count
			same_slot_count: used_slot_count = old used_slot_count
			replaced_or_conflict_or_not_found: replaced or conflict or not_found
			old_absent: (replaced and not equal (new_key, old_key)) implies (not has (old_key))
			new_present: (replaced or conflict) = has (new_key)
			new_item: replaced implies (item (new_key) = old (item (old_key)))
			not_found_iff_no_old_key: not_found = old (not has (old_key))
			conflict_iff_already_present: conflict = old (has (new_key))
			not_inserted_if_conflict: conflict implies (item (new_key) = old (item (new_key)))
			default_property: has_default = ((new_key = computed_default_key) or ((new_key /= computed_default_key) and (old has_default)))

feature -- Removal

	clear_all
			-- Reset all items to default values; reset status.
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			wiped_out: is_empty
		ensure then
			position_equal_to_zero: position = 0
			count_equal_to_zero: count = 0
			used_slot_count_equal_to_zero: used_slot_count = 0
			has_default_set: not has_default
			no_status: not special_status

	remove (key: H)
			-- Remove item associated with key, if present.
			-- Set removed if and only if an item has been
			-- removed (i.e. key was present);
			-- if so, set position to index of removed element.
			-- If not, set not_found.
		ensure
			removed_or_not_found: removed or not_found
			not_present: not has (key)
			one_less: found implies (count = old count - 1)
			same_slot_count: used_slot_count = old used_slot_count
			default_case: (key = computed_default_key) implies (not has_default)
			non_default_case: (key /= computed_default_key) implies (has_default = old has_default)

feature -- Conversion

	linear_representation: ARRAYED_LIST [G]
			-- Representation as a linear structure
		ensure then
			result_exists: Result /= void
			good_count: Result.count = count

feature -- Duplication

	copy (other: like Current)
			-- Re-initialize from other.
		require -- from ANY
			other_not_void: other /= void
			type_identity: same_type (other)
		ensure -- from ANY
			is_equal: is_equal (other)

invariant

	keys_not_void: keys /= void
	content_not_void: content /= void
	keys_same_capacity_plus_one: keys.count = capacity + 1
	content_same_capacity_plus_one: content.count = capacity + 1
	deleted_same_capacity: deleted_marks.count = capacity
	keys_starts_at_zero: keys.lower = 0
	content_starts_at_zero: content.lower = 0
	deleted_starts_at_zero: deleted_marks.lower = 0
	valid_iteration_position: off or truly_occupied (iteration_position)
	control_non_negative: control >= 0
	special_status: special_status = (conflict or inserted or replaced or removed or found or not_found)
	max_occupation_meaningful: (max_occupation > 0) and (max_occupation < 100)
	initial_occupation_meaningful: (initial_occupation > 0) and (initial_occupation < 100)
	sized_generously_enough: initial_occupation < max_occupation
	count_big_enough: 0 <= count
	count_small_enough: count <= capacity
	breathing_space: count * 100 <= capacity * max_occupation
	count_no_more_than_slot_count: count <= used_slot_count
	slot_count_big_enough: 0 <= count
	slot_count_small_enough: used_slot_count <= capacity
	extra_space_non_negative: extra_space >= 0
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from FINITE
	empty_definition: is_empty = (count = 0)
	non_negative_count: count >= 0

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 HASH_TABLE