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

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

Mar 14, 2023 43 likes •838 views

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

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SHEEP CLONING

Paley Li, Nicholas Cameron, and James Noble

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Object cloning

  • How do you do object cloning?

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Shallow cloning

  • Copies an object and alias the references in that object.

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Shallow cloning

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foo a b

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

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foo’ b a foo a b

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

  • Copies the object and its referenced objects.

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Deep cloning

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  • Copies the object and its referenced objects.

foo a b

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Deep cloning

  • Copies the object and its referenced objects.

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a foo b a foo’ b

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  • Shallow cloning is too shallow

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displayWindow

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scrollBar

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  • Shallow cloning is too shallow

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displayWindow

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scrollBar displayWindow’

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  • Shallow cloning is too shallow

displayWindow displayWindow’

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  • Deep cloning is too deep

displayWindow imageDatabase

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  • Deep cloning is too deep

displayWindow imageDatabase displayWindow’ imageDatabase’

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  • Deep cloning is too deep

displayWindow displayWindow’

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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.

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Common practices

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  • Cloning in C++ :
  • Copy constructors and assignment operators.
  • Cloning in Eiffel :
  • Inherit shallow and deep cloning from the

ANY class.

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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?

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  • 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.

  • Only copy those “important” areas.

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  • The ideal model
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Ownership Types

  • Ownership types enforce a hierarchical topology over the

heap.

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  • Context is the formal set of objects owned by an object.
  • Representation is the set of objects which are

conceptually part of an object.

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Ownership Types

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  • Context is the formal set of objects owned by an object.
  • Representation is the set of objects which are

conceptually part of an object.

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Ownership Types

Representation = context =

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Deep Ownership

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

X X

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Deep Ownership

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

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  • Sheep cloning is just right!

displayWindow

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  • Sheep cloning is just right!

displayWindow displayWindow’

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  • Sheep cloning is just right!

displayWindow displayWindow’

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  • Sheep cloning is just right!

displayWindow displayWindow’

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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.

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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A touch of formal

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Original object

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A touch of formal

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Original object

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A touch of formal

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Original object

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A touch of formal

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Original heap

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A touch of formal

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Map

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A touch of formal

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Sheep clone

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A touch of formal

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New heap (containing the Sheep clone)

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A touch of formal

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  • SheepAux function:
  • R-SheepInside: Copies the object if it is inside the original
  • bject.
  • R-SheepOutside: Creates an alias to the object if the object is
  • utside the original object.
  • R-SheepRef: Creates a reference to an existing Sheep clone of an
  • bject using the Map.
  • R-SheepNull: Returns a null, when Sheep cloning a null.
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Can we clone it?

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B A C D

  • Lets Sheep clone object A.
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Can we clone it?

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  • R-SheepInside creates the object A’ by copying A.

B A C D A’ Map: A A’

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Can we clone it?

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  • R-SheepOutside creates an alias to D.

B A C D A’ Map: A A’ D D

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Can we clone it?

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  • R-SheepInside creates the object B’ by copying B.

B A C D A’ Map: A A’ D D B B’ B’

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Can we clone it?

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  • R-SheepInside creates the object C’ by copying C.

B A C D A’ B’ C’ Map: A A’ D D B B’ C C’

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…. Yes we can!

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  • R-SheepRef creates the reference from object C’ to
  • bject B’ using the map.

B A C D A’ B’ C’ Map: A A’ D D B B’ C C’

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Proving the formalism

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Proving the formalism

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Proving the formalism

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Proving the formalism

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Proving the formalism

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Proving the formalism

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Correctness of the formalism

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B A C D A’ B’ C’ = A Where: = A’

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Correctness of the formalism

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B A C D A’ B’ C’ = A Where: = A’

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Correctness of the formalism

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B A C D A’ B’ C’

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Correctness of the formalism

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B A C D A’ B’ C’

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Correctness of the formalism

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B A C D A’ B’ C’

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Correctness of the formalism

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B A C D A’ B’ C’

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Correctness of the formalism

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B A C D A’ B’ C’ A’’ A’

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Correctness of the formalism

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B A C D A’ B’ C’ B’ A’, C’’ A’

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Correctness of the formalism

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B A C D A’ B’ C’ A ’ D

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Correctness of the formalism

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B A C D A’ B’ C’ A’ D

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Correctness of the formalism

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B A C A’ B’ C’ D

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Correctness of the formalism

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B A C A’ B’ C’ A ’ D D

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Correctness of the formalism

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B A C D A’ B’ C’ A’ ’ D

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Correctness of the formalism

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B A C A’ B’ C’ D A’ ’ D

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Correctness of the formalism

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B A C D A’ B’ C’

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Correctness of the formalism

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B A C D A’ B’ C’

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Correctness of the formalism

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B A C D A’ B’ C’

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Summary

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

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Thank you. Questions?

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