SHEEP CLONING Paley Li, Nicholas Cameron, and James Noble 2 Object - PowerPoint PPT Presentation

1 SHEEP CLONING Paley Li, Nicholas Cameron, and James Noble

2 Object cloning • How do you do object cloning?

3 Shallow cloning • Copies an object and alias the references in that object.

3 Shallow cloning • Copies an object and alias the references in that object. foo a b

3 Shallow cloning • Copies an object and alias the references in that object. foo ’ foo a a b b

4 Deep cloning • Copies the object and its referenced objects.

4 Deep cloning • Copies the object and its referenced objects. foo a b

4 Deep cloning • Copies the object and its referenced objects. foo ’ foo a a b b

5 - Shallow cloning is too shallow displayWindow scrollBar 9

5 - Shallow cloning is too shallow displayWindow ’ displayWindow scrollBar 10

6 - Shallow cloning is too shallow displayWindow ’ displayWindow 11

7 - Deep cloning is too deep displayWindow imageDatabase

7 - Deep cloning is too deep displayWindow ’ displayWindow imageDatabase’ imageDatabase

8 - Deep cloning is too deep displayWindow ’ displayWindow

9 Common practices • Cloning in Java (Cloneable) and C# (ICloneable): • Default clone() method is shallow. • Defining deep cloning is inconvenient and prone to bugs. • Requires type casting.

10 Common practices • Cloning in C++ : • Copy constructors and assignment operators. • Cloning in Eiffel : • Inherit shallow and deep cloning from the ANY class.

11 Common practices • Most practices still suffer from the flaws of shallow and deep cloning. • Not automated. • “Programmer knows best” - they have to define their own cloning. • What if we have the information to produce more sensible clones, but had overlooked it?

12 - The ideal model • We aim to formalise a cloning model that is just right. • It needs to be able to identify areas that are “important” to an object. • O nly copy those “important” areas.

13 Ownership Types • Ownership types enforce a hierarchical topology over the heap.

14 Ownership Types • Context is the formal set of objects owned by an object. • Representation is the set of objects which are conceptually part of an object.

14 Ownership Types • Context is the formal set of objects owned by an object. • Representation is the set of objects which are conceptually part of an object. Representation = context =

15 Deep Ownership • All reference paths to an object must pass through that object’s owner. • Also known as owners-as-dominators. X X

15 Deep Ownership • All reference paths to an object must pass through that object’s owner. • Also known as owners-as-dominators.

16 Sheep = Shallow + Deep • Utilises ownership types to identify the “important bits” of each object. • Cloning an object’s representation: • Copies every object inside the object’s context. • Aliases every reference to objects outside the object’s context.

17 - Sheep cloning is just right! displayWindow

17 - Sheep cloning is just right! displayWindow ’ displayWindow

17 - Sheep cloning is just right! displayWindow ’ displayWindow

17 - Sheep cloning is just right! displayWindow ’ displayWindow

18 Sheep cloning • We have formalised sheep cloning in an ownership system with deep ownership. • We have proved soundness and an assortment of correctness property of our formalism.

19 A touch of formal

19 A touch of formal

19 A touch of formal

19 A touch of formal

19 A touch of formal

19 A touch of formal

19 A touch of formal

19 A touch of formal

19 A touch of formal

20 A touch of formal

21 A touch of formal

21 A touch of formal Original object

21 A touch of formal Original object

21 A touch of formal Original object

21 A touch of formal Original heap

21 A touch of formal Map

21 A touch of formal Sheep clone

21 A touch of formal New heap (containing the Sheep clone)

22 A touch of formal • SheepAux function: • R-SheepInside : Copies the object if it is inside the original object. • R-SheepOutside : Creates an alias to the object if the object is outside the original object. • R-SheepRef : Creates a reference to an existing Sheep clone of an object using the Map . • R-SheepNull : Returns a null, when Sheep cloning a null.

23 Can we clone it? • Lets Sheep clone object A. D A C B

23 Can we clone it? • R-SheepInside creates the object A ’ by copying A. D A ’ A C B Map: A A ’

23 Can we clone it? • R-SheepOutside creates an alias to D. D A ’ A C B Map: A A ’ D D

23 Can we clone it? • R-SheepInside creates the object B ’ by copying B. D A ’ A C B ’ B Map: A A ’ D D B B ’

23 Can we clone it? • R-SheepInside creates the object C ’ by copying C. D A ’ A C ’ C B ’ B Map: A A ’ D D B B ’ C C ’

23 …. Yes we can! • R-SheepRef creates the reference from object C ’ to object B ’ using the map. D A ’ A C ’ C B ’ B Map: A A ’ D D B B ’ C C ’

24 Proving the formalism

24 Proving the formalism

25 Proving the formalism

25 Proving the formalism

25 Proving the formalism

25 Proving the formalism

26 Correctness of the formalism Where: = A = A ’ D A ’ A C ’ C B ’ B

26 Correctness of the formalism Where: = A = A ’ D A ’ A C ’ C B ’ B

27 Correctness of the formalism D A ’ A C ’ C B ’ B

27 Correctness of the formalism D A ’ A C ’ C B ’ B

27 Correctness of the formalism D A ’ A C ’ C B ’ B

28 Correctness of the formalism D A ’ A C ’ C B ’ B

28 Correctness of the formalism A ’ ’ A ’ D A ’ A C ’ C B ’ B

28 Correctness of the formalism B ’ A ’ , C ’ ’ A ’ D A ’ A C ’ C B ’ B

29 Correctness of the formalism A ’ D D A ’ A C ’ C B ’ B

29 Correctness of the formalism A ’ D D A ’ A C ’ C B ’ B

30 Correctness of the formalism D A ’ A C ’ C B ’ B

30 Correctness of the formalism A ’ D D A ’ A C ’ C B ’ B

31 Correctness of the formalism A ’ ’ D D A ’ A C ’ C B ’ B

31 Correctness of the formalism A ’ ’ D D A ’ A C ’ C B ’ B

32 Correctness of the formalism D A ’ A C ’ C B ’ B

32 Correctness of the formalism D A ’ A C ’ C B ’ B

32 Correctness of the formalism D A ’ A C ’ C B ’ B

33 Summary • Shallow is too shallow. • Deep is too deep. • Sheep = shallow + deep. • Formalised sheep cloning. • Proved soundness and correctness.

34 Thank you. Questions?