note
	description: "Summary description for {REGISTRATION}."
	author: ""
	date: "$Date$"
	revision: "$Revision$"

class 
	REGISTRATION

create 
	default_create

feature -- Access

	generating_type: TYPE [detachable REGISTRATION]
			-- Type of current object
			-- (type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generating_type_not_void: Result /= Void
		end

	generator: STRING_8
			-- Name of current object's generating class
			-- (base class of the type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generator_not_void: Result /= Void
			generator_not_empty: not Result.is_empty
		end
	
feature -- Comparison

	frozen deep_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void
			-- or attached to isomorphic object structures?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_deep_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			shallow_implies_deep: standard_equal (a, b) implies Result
			both_or_none_void: (a = Void) implies (Result = (b = Void))
			same_type: (Result and (a /= Void)) implies (b /= Void and then a.same_type (b))
			symmetric: Result implies deep_equal (b, a)
		end

	frozen equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached
			-- to objects considered equal?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.is_equal (b))
		end

	frozen is_deep_equal (other: REGISTRATION): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			shallow_implies_deep: standard_is_equal (other) implies Result
			same_type: Result implies same_type (other)
			symmetric: Result implies other.is_deep_equal (Current)
		end

	is_equal (other: REGISTRATION): BOOLEAN
			-- Is other attached to an object considered
			-- equal to current object?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result
		end

	frozen standard_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached to
			-- field-by-field identical objects of the same type?
			-- Always uses default object comparison criterion.
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.standard_is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.standard_is_equal (b))
		end

	frozen standard_is_equal (other: REGISTRATION): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object, and field-by-field identical to it?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)
		end
	
feature -- Status report

	conforms_to (other: ANY): BOOLEAN
			-- Does type of current object conform to type
			-- of other (as per Eiffel: The Language, chapter 13)?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		end

	same_type (other: ANY): BOOLEAN
			-- Is type of current object identical to type of other?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))
		end
	
feature -- Duplication

	frozen clone (other: detachable ANY): like other
		obsolete "Use `twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- equal to other
			--
			-- For non-void other, clone calls copy;
			-- to change copying/cloning semantics, redefine copy.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.twin
			end
		ensure -- from ANY
			instance_free: class
			equal: Result ~ other
		end

	copy (other: REGISTRATION)
			-- Update current object using fields of object attached
			-- to other, so as to yield equal objects.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_equal: Current ~ other
		end

	frozen deep_clone (other: detachable ANY): like other
		obsolete "Use `deep_twin' instead. [2017-05-31]"
			-- Void if other is void: otherwise, new object structure
			-- recursively duplicated from the one attached to other
			-- (from ANY)
		do
			if other /= Void then
				Result := other.deep_twin
			end
		ensure -- from ANY
			instance_free: class
			deep_equal: deep_equal (other, Result)
		end

	frozen deep_copy (other: REGISTRATION)
			-- Effect equivalent to that of:
			--		copy (other . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		do
			copy (other.deep_twin)
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)
		end

	frozen deep_twin: REGISTRATION
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)
		end

	frozen standard_clone (other: detachable ANY): like other
		obsolete "Use `standard_twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.standard_twin
			end
		ensure -- from ANY
			instance_free: class
			equal: standard_equal (Result, other)
		end

	frozen standard_copy (other: REGISTRATION)
			-- Copy every field of other onto corresponding field
			-- of current object.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)
		end

	frozen standard_twin: REGISTRATION
			-- New object field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)
		end

	frozen twin: REGISTRATION
			-- New object equal to Current
			-- twin calls copy; to change copying/twinning semantics, redefine copy.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result ~ Current
		end
	
feature -- Basic operations

	frozen as_attached: attached REGISTRATION
		obsolete "Remove calls to this feature. [2017-05-31]"
			-- Attached version of Current.
			-- (Can be used during transitional period to convert
			-- non-void-safe classes to void-safe ones.)
			-- (from ANY)
		do
			Result := Current
		end

	frozen default: detachable REGISTRATION
			-- Default value of object's type
			-- (from ANY)
		do
		end

	frozen default_pointer: POINTER
			-- Default value of type POINTER
			-- (Avoid the need to write p.default for
			-- some p of type POINTER.)
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end

	default_rescue
			-- Process exception for routines with no Rescue clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end

	frozen do_nothing
			-- Execute a null action.
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end
	
feature -- Attributes

	registrations: REL [STUDENT, COURSE]
	
feature -- Auxiliary functions

	conflict (c1, c2: COURSE): BOOLEAN
			-- Do courses 'c1' and 'c2' conflict with each other?
		do
			Result := (c1.day = c2.day) and then ((c1.start ~ c2.start or (c1.start < c2.start and then c1.start + c1.duration >= c2.start) or (c2.start < c1.start and then c2.start + c2.duration >= c1.start)))
		ensure
				Result = ((c1.day = c2.day) and ((c1.start ~ c2.start or (c1.start < c2.start and c1.start + c1.duration >= c2.start) or (c2.start < c1.start and c2.start + c2.duration >= c1.start))))
		end

	no_conflicts (regs: REL [STUDENT, COURSE]): BOOLEAN
			-- ∀ (s1, c1), (s2, c2) ∈ regs :
			--       c1 ≠ c2 ⋀ s1 = s2 ⇒ ¬(conflict (c1, c2))
		local
			it1, it2: ITERATION_CURSOR [PAIR [STUDENT, COURSE]]
			c1, c2: COURSE
			s1, s2: STUDENT
		do
			Result := True
			from
				it1 := regs.new_cursor
			until
				not Result or else it1.after
			loop
				from
					it2 := regs.new_cursor
				until
					not Result or else it2.after
				loop
					s1 := it1.item.first
					c1 := it1.item.second
					s2 := it2.item.first
					c2 := it2.item.second
					if c1 /~ c2 and then s1 ~ s2 and then conflict (c1, c2) then
						Result := False
					end
					it2.forth
				end
				it1.forth
			end
		ensure
				Result = across
					regs as r1
				all
					across
						regs as r2
					all
						r1.item /~ r2.item and r1.item.first ~ r2.item.first implies not (conflict (r1.item.second, r2.item.second))
					end
				end
		end
	
feature -- Auxiliary functions for contracts

	pair (s: STUDENT; c: COURSE): PAIR [STUDENT, COURSE]
		do
			create Result.make (s, c)
		end
	
feature -- Commands for registrations

	extend (s: STUDENT; c: COURSE)
			-- Register student 's' for course 'c'.
		require
			not_registered_yet: not registrations.has (pair (s, c))
			no_conflicting_registrations: no_conflicts (registrations + pair (s, c))
		do
			registrations.extend (pair (s, c))
		ensure
				registrations ~ old registrations.deep_twin.extended (pair (s, c))
		end

	extend_by_array (a: ARRAY [TUPLE [s: STUDENT; c: COURSE]])
			-- Register the list of students and courses.
		require
			not_registered_yet: across
					a as it
				all
					not registrations.has (pair (it.item.s, it.item.c))
				end
			no_conflicting_registrations: no_conflicts (registrations.unioned (create {REL [STUDENT, COURSE]}.make_from_tuple_array (a)))
		do
			across
				a as it
			loop
				extend (it.item.s, it.item.c)
			end
		ensure
				registrations ~ old registrations.deep_twin.unioned (create {REL [STUDENT, COURSE]}.make_from_tuple_array (a))
		end

	remove (s: STUDENT; c: COURSE)
			-- Unregister student 's' for course 'c'.
		require
				registrations.has (pair (s, c))
		do
			registrations.subtract (pair (s, c))
		ensure
				registrations ~ old registrations.deep_twin.subtracted (pair (s, c))
		end
	
feature -- Constructor

	default_create
			-- Process instances of classes with no creation clause.
			-- (Default: do nothing.)
		do
			create registrations.make_empty
		end
	
feature -- Output

	Io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)
		once
			create Result
			Result.set_output_default
		ensure -- from ANY
			instance_free: class
			io_not_void: Result /= Void
		end

	out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		do
			Result := tagged_out
		ensure -- from ANY
			out_not_void: Result /= Void
		end

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		do
			if o /= Void then
				Io.put_string (o.out)
			end
		ensure -- from ANY
			instance_free: class
		end

	frozen tagged_out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			tagged_out_not_void: Result /= Void
		end
	
feature -- Platform

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		once
			create Result
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
		end
	
feature -- Queries

	Max_course_load: INTEGER_32 = 3
	
feature {NONE} -- Retrieval

	frozen internal_correct_mismatch
			-- Called from runtime to perform a proper dynamic dispatch on correct_mismatch
			-- from MISMATCH_CORRECTOR.
			-- (from ANY)
		local
			l_msg: STRING_8
			l_exc: EXCEPTIONS
		do
			if attached {MISMATCH_CORRECTOR} Current as l_corrector then
				l_corrector.correct_mismatch
			else
				create l_msg.make_from_string ("Mismatch: ")
				create l_exc
				l_msg.append (generating_type.name)
				l_exc.raise_retrieval_exception (l_msg)
			end
		end
	
invariant
	max_course_load: across
			registrations as r
		all
			# registrations.image (r.item.first) <= Max_course_load
		end
	no_conflicting_registrations: no_conflicts (registrations)

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

end -- class REGISTRATION

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