sheep cloning
DESCRIPTION
Sheep Cloning. Paley Li, Nicholas Cameron, and James Noble. Object cloning. How do you do object cloning?. Shallow cloning. Copies an object and alias the references in that object. Shallow cloning. Copies an object and alias the references in that object. foo . a. b. - PowerPoint PPT PresentationTRANSCRIPT
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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.
Shallow cloning
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foo a
b
• Copies an object and alias the references in that object.
Shallow cloning
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foo’
b
afoo
a
b
• Copies an object and alias the references in that object.
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
Deep cloning• Copies the object and its referenced objects.
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afoo
b
afoo’
b
- Shallow cloning is too shallow
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displayWindow
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scrollBar
- Shallow cloning is too shallow
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displayWindow
5
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’
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.
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
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
• 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 =
Deep Ownership
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• All reference paths to an object must pass through that object’s owner.
• Also known as owners-as-dominators.
X
X
Deep Ownership
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• All reference paths to an object must pass through that object’s owner.
• Also known as owners-as-dominators.
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’
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
A touch of formal
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Original object
A touch of formal
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Original object
A touch of formal
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Original heap
A touch of formal
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Map
A touch of formal
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Sheep clone
A touch of formal
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New heap (containing the Sheep clone)
A touch of formal
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• 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.
Can we clone it?
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B
A
C
D
• Lets Sheep clone object A.
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’
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
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’
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’
…. Yes we can!
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• R-SheepRef creates the reference from object C’ to object B’ using the map.
B
A
C
D
A’
B’C’
Map: A A’ D D B B’ C C’
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’
= AWhere:= A’
Correctness of the formalism
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B
A
C
D
A’
B’C’
= AWhere:= A’
Correctness of the formalism
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B
A
C
D
A’
B’C’
Correctness of the formalism
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B
A
C
D
A’
B’C’
Correctness of the formalism
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B
A
C
D
A’
B’C’
Correctness of the formalism
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B
A
C
D
A’
B’C’
Correctness of the formalism
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B
A
C
D
A’
B’C’
A’’ A’
Correctness of the formalism
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B
A
C
D
A’
B’C’
B’ A’, C’’ A’
Correctness of the formalism
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B
A
C
D
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B’C’
A ’ D
Correctness of the formalism
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B
A
C
D
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B’C’
A’ D
Correctness of the formalism
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B
A
C
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B’C’
D
Correctness of the formalism
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B
A
C
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B’C’
A ’ D
D
Correctness of the formalism
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B
A
C
D
A’
B’C’
A’ ’ D
Correctness of the formalism
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B
A
C
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D
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Correctness of the formalism
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B
A
C
D
A’
B’C’
Correctness of the formalism
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B
A
C
D
A’
B’C’
Correctness of the formalism
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B
A
C
D
A’
B’C’
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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