indexing
	description: "References to objects containing a character value"
	status: "See notice at end of class"
	date: "$Date$"
	revision: "$Revision$"

class interface
	CHARACTER_REF

feature -- Access

	code: INTEGER
			-- Associated integer value

	hash_code: INTEGER
			-- Hash code value
		ensure -- from HASHABLE
			good_hash_value: Result >= 0

	item: CHARACTER
			-- Character value

	Max_value: INTEGER is 255
			-- Bounds for integer representation of characters (ASCII)

	Min_value: INTEGER is 0
	
feature -- Comparison

	is_equal (other: like Current): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object and identical to it?
		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 COMPARABLE
			trichotomy: Result = (not (Current < other) and not (other < Current))

	max (other: like Current): like Current
			-- The greater of current object and other
			-- (from COMPARABLE)
		require -- from COMPARABLE
			other_exists: other /= void
		ensure -- from COMPARABLE
			current_if_not_smaller: Current >= other implies Result = Current
			other_if_smaller: Current < other implies Result = other

	min (other: like Current): like Current
			-- The smaller of current object and other
			-- (from COMPARABLE)
		require -- from COMPARABLE
			other_exists: other /= void
		ensure -- from COMPARABLE
			current_if_not_greater: Current <= other implies Result = Current
			other_if_greater: Current > other implies Result = other

	three_way_comparison (other: CHARACTER_REF): INTEGER
			-- If current object equal to other, 0;
			-- if smaller, -1; if greater, 1
		require -- from COMPARABLE
			other_exists: other /= void
		ensure -- from COMPARABLE
			equal_zero: (Result = 0) = is_equal (other)
			smaller_negative: (Result = - 1) = (Current < other)
			greater_positive: (Result = 1) = (Current > other)

	infix "<" (other: like Current): BOOLEAN
			-- Is other greater than current character?
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then -- from COMPARABLE
			asymmetric: Result implies not (other < Current)
		ensure then
			definition: Result = (code < other.code)

	infix "<=" (other: like Current): BOOLEAN
			-- Is current object less than or equal to other?
			-- (from COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then -- from COMPARABLE
			definition: Result = ((Current < other) or is_equal (other))

	infix ">" (other: like Current): BOOLEAN
			-- Is current object greater than other?
			-- (from COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then -- from COMPARABLE
			definition: Result = (other < Current)

	infix ">=" (other: like Current): BOOLEAN
			-- Is current object greater than or equal to other?
			-- (from COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then -- from COMPARABLE
			definition: Result = (other <= Current)
	
feature -- Status report

	is_alpha: BOOLEAN
			-- Is item alphabetic?
			-- Alphabetic is is_upper or is_lower

	is_digit: BOOLEAN
			-- Is item a digit?
			-- A digit is one of 0123456789

	is_hashable: BOOLEAN
			-- May current object be hashed?
			-- (True if it is not its type's default.)
		ensure -- from HASHABLE
			ok_if_not_default: Result implies (Current /= default)

	is_lower: BOOLEAN
			-- Is item lowercase?

	is_upper: BOOLEAN
			-- Is item uppercase?
	
feature -- Element change

	set_item (c: CHARACTER)
			-- Make c the item value.
	
feature -- Conversion

	lower: CHARACTER
			-- Lowercase value of item
			-- Returns item if not is_upper

	upper: CHARACTER
			-- Uppercase value of item
			-- Returns item if not is_lower
	
feature -- Basic routines

	next: CHARACTER
			-- Next character
		require
			valid_character: (item.code + 1).is_valid_character_code
		ensure
			valid_result: Result |-| item = 1

	previous: CHARACTER
			-- Previous character
		require
			valid_character: (item.code - 1).is_valid_character_code
		ensure
			valid_result: Result |-| item = - 1

	infix "+" (incr: INTEGER): CHARACTER
			-- Add incr to the code of item
		require
			valid_increment: (item.code + incr).is_valid_character_code
		ensure
			valid_result: Result |-| item = incr

	infix "-" (decr: INTEGER): CHARACTER
			-- Subtract decr to the code of item
		require
			valid_decrement: (item.code - decr).is_valid_character_code
		ensure
			valid_result: item |-| Result = decr

	infix "|-|" (other: CHARACTER): INTEGER
			-- Difference between the codes of item and other
		ensure
			valid_result: other + Result = item
	
feature -- Output

	out: STRING
			-- Printable representation of character
	
invariant

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from COMPARABLE
	irreflexive_comparison: not (Current < Current)

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 CHARACTER_REF