Changeable class and pattern to provide selective mutability in computer programming environments

• US 7,219,340 B2
• Filed: 10/23/2003
• Issued: 05/15/2007
• Est. Priority Date: 10/23/2003
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Schechter, Greg D., Beda, Joseph S.
• Primary Examiner(s): CHAVIS, JOHN Q
• Application Number:
  US10/693,438
• Publication Number:
  US 20050091637A1
• Time in Patent Office: 1,300 Days
• Field of Search: 717/144, 717/125, 717/126, 717/108
• US Class Current: 717/144
• CPC Class Codes: G06F 8/31 Programming languages or programming paradigms

Abstract

A changeable pattern and implementation is presented in which types (used in programming environments and virtual machines) may be mutable as controlled by a programmer, and share many of the benefits of value types, without the drawbacks of value types. The changeable pattern provides flexibility for restricting the modifiability of the resultant uses of the values, as well as providing a means for providing notifications upon changes. In one implementation, a single set of changeable types is provided that derive from a common Changeable base class, and any type for which mutability is desired may derive from the Changeable class. Properties associated with the changeable define state that determines cloning and/or changeability characteristics on subsequent uses of the type. True mutability is provided via a status property of next use being set to a changeable reference state such that subsequent uses of the type do not cause a state change.

Claims

1. In a computing environment, a method comprising:

maintaining a base class, the base class comprising two properties, isChangeable and statusOfNextUse;

receiving a request for a type, the type deriving from the base class and inheriting the properties of the base class;

causing the type to be created, and upon being created, the type'"'"'s isChangeable property set to allow a change, and the type'"'"'s statusOfNextUse property set not to allow a change upon a next qualified use; and

upon a next qualified use, causing the type to be cloned, the cloned type having an isChangable property set not to allow a change.

2. The method of claim 1 further comprising, receiving a request to copy the type, and in response, causing the type to be cloned, the cloned type having a changeable property set to allow a change and a status property set to allow a change upon a next qualified use.

3. The method of claim 2 further comprising, receiving a request to copy the cloned type, and in response, causing the cloned type to be cloned into a second cloned type, the second cloned type having a changeable property set to allow a change and a status property set to not allow a change upon a next qualified use.

4. The method of claim 1 further comprising, receiving a request to set the type to not allow a change, and in response, causing the type to have the changeable property not allow a change.

5. The method of claim 4 wherein the type has an associated object tree, and further comprising, recursively setting property data in the object tree to not allow a change to any object in the tree.

6. The method of claim 4 further comprising, receiving a request to copy the type, and in response, causing the type to be cloned, the cloned type having a changeable property set to allow a change and a status property set to not allow a change upon a next qualified use.

7. The method of claim 1 further comprising, receiving a request directed towards whether a changeable object is allowed to be made unchangeable, determining whether the changeable object is allowed to made unchangeable, and returning a response to the request based on that determination.

8. The method of claim 1 further comprising, receiving a request to modify the status property to allow a changeable copy, and in response, causing the type to have the status property set to a state in which the type is cloned upon a next qualified use, the cloned type having a changeable property set to allow a change and a status property set to not allow a change.

9. The method of claim 1 further comprising, receiving a request to modify the status property to allow a changeable reference, and further comprising, causing the type to have the status property set to allow a change upon a next qualified use.

10. The method of claim 9 further comprising, providing a notification of the change upon the next qualified use.

11. The method of claim 10 wherein providing the notification comprises propagating event handlers hierarchically down the type, such that a deep node need not communicate with a parent node to provide a notification associated with the type when the deep object has changed.

12. The method of claim 1 further comprising, determining whether a next us is a qualified use.

13. A computer-readable medium having computer-executable instructions, which, when executed, perform the method of claim 1.

14. In a computing environment, a method comprising:

providing a type, the type comprising properties isChangeable and statusOfNextUse, the isChangeable property set to allow a change and the statusOfNextUse property set to changeableReference; and

upon receiving a request to change data of the type in a qualified use, and based on the isChangeable property and statusOfNextUse property, allowing the data to change in the type and leaving the type in the changeableReference state.

15. The method of claim 14 further comprising, causing a notification of the change to be provided.

16. The method of claim 15 wherein the change is to a hierarchically deep node in the type having an event handler propagated thereto, and wherein providing the notification comprises sending the notification from the deep node based on the event handler without the deep node having to have knowledge of a parent node.

17. The method of claim 14 further comprising, receiving a request requesting whether a changeable object is allowed to be made unchangeable, determining whether the changeable object is allowed to made unchangeable, and returning a response to the request based on that determination.

18. The method of claim 17 wherein the changeable object is allowed to made unchangeable, and further comprising, receiving a request to modify the status property to an unchangeable setting, and in response, causing the type to enter another state in which the changeable property is set to changeable and the status property is set to unchangeable upon a next qualified use.

19. The method of claim 14 further comprising, receiving a request to modify the status property to a changeable copy, and in response, causing the type to enter a changeable copy state in which upon a subsequent qualified use, a cloned type is made having a changeable property set to allow a change and a status property set to not allow a subsequent change.

20. A computer-readable medium having computer-executable instructions, which, when executed, perform the method of claim 14.

21. A computer-readable medium having stored thereon a data structure, the data structure comprising:

a data field representing a first property having data corresponding to whether a type is changeable or unchangeable;

a data field representing a second property having data corresponding to a state of the type upon a subsequent use; and

wherein when the first property corresponds to a changeable state;

1) when the second property has a setting corresponding to unchangeable, a qualified use of the type causes a clone to be created, the clone having a first property that is set to unchangeable;

2) when the second property has a setting corresponding to changeable copy, a qualified use of the type causes a clone to be created having a first property that is set to make the clone changeable and a second property set to unchangeable such that a subsequent use of the clone will create another clone, the other clone having a first property that corresponds to unchangeable; and

3) when the second property has a setting corresponding to changeable reference, a qualified use of the type remains in a state in which the first property corresponds to a changeable state and the a second property setting corresponds to changeable reference.

22. The data structure of claim 21 further comprising a copy method that when invoked causes a causes a clone to be created, the clone having a first property that is set to changeable and a second property set to unchangeable such that a subsequent use of the clone will create another clone, the other clone having a first property that corresponds to unchangeable.

23. The data structure of claim 21 further comprising a method that when invoked causes the first property to change from the changeable state to the unchangeable state.

24. The data structure of claim 21 further comprising a method that when invoked causes the second property setting to change from unchangeable to changeable copy.

25. The data structure of claim 21 further comprising a method that when invoked causes the second property setting to change from unchangeable to changeable reference.

26. The data structure of claim 21 further comprising a method that when invoked causes the second property setting to change from changeable copy to unchangeable.

27. The data structure of claim 21 further comprising a method that when invoked causes the second property setting to change from changeable reference to unchangeable.

28. The data structure of claim 21 further comprising a method that when invoked causes the second property setting to change from changeable reference to changeable copy.

29. The data structure of claim 21 further comprising a method that when invoked causes the second property setting to change from changeable copy to changeable reference.

30. The data structure of claim 21 further comprising a third property indicative of whether the data structure can be made unchangeable while ensuring consistency, and a method that when invoked causes a response corresponding to the third field.

31. In a computing environment, a system comprising:

means for maintaining a parent class from which a type subclass may derive, the parent class comprising properties isChangeable and statusOtNextUse;

means for providing a type corresponding to a subclass of the parent class, the subclass further comprising contained data;

means for setting the type into one of a plurality of states defined by settings of the properties of the parent class associated with the type;

means for receiving a request to change the contained data of the type in a qualified use; and

means for determining how to process the request based on the property settings.

32. The system of claim 31 wherein one of the plurality of states comprises a changeable reference state in which a changeable property allows a change, and a status property specifies that the type is a changeable reference, and wherein the means for determining how to process the request allows the change and leaves the type in the changeable reference state.

33. The system of claim 32 further comprising, means for causing a notification of the change to be provided.

34. The system of claim 31 further comprising, means for receiving a request to modify the status property to an unchangeable setting, and means for causing the type to enter a state in which the changeable property set to allow a change and the status property set to not allow a change upon a next qualified use.

35. The system of claim 31 further comprising, means for receiving a request to modify the status property to a changeable copy, and means for causing the type to enter a changeable copy state in which upon a subsequent qualified use, a cloned type is made having a changeable property set to allow a change and a status property set to not allow a subsequent change.

36. In a computing environment, a method comprising:

receiving a request to copy a type, the type being derived from a parent class, the type containing hierarchically deep data;

in response to the request, causing a shallow copy of the type to be created, the shallow copy not containing the hierarchically deep data upon being created; and

upon access to at least some of the hierarchically deep data being requested, copying the at least some of the hierarchically deep data to the shallow copy to enable the shallow copy to act as a deep copy.

37. In a computing environment, a method comprising:

receiving a request related to a type, the type having a first property corresponding to whether that type is changeable or unchangeable and having a second property corresponding to a state of the type upon a subsequent use;

determining whether the request corresponds to a qualified use; and

when the request corresponds to a qualified use and the first property corresponds to a changeable state;

1) when the second property has a setting corresponding to unchangeable, causing a clone of the type to be created, the clone having a first property that is set to unchangeable;

2) when the second property has a setting corresponding to changeable copy, causing a clone of the type to be created having a first property that is set to changeable and a second property set to unchangeable such that a subsequent qualified use of the clone will create a clone of the clone, the clone of the clone having a first property that is set to make the clone of the clone changeable and a second property set such that a subsequent use of the clone of the clone will make the clone of the clone unchangeable; and

3) when the second property has a setting corresponding to changeable reference, remaining in a state in which the first property corresponds to a changeable state and the a second property setting corresponds to changeable reference.

38. In a computing environment, a method comprising:

providing a reference object, the reference object having a first property corresponding to whether the reference object is changeable or unchangeable and a second property corresponding to a state of the reference object upon a subsequent use; and

using the property values to determine a state of the reference object following a qualified use such that the reference object includes characteristics of a value type wherein a shallow copy is created of the reference object on cloning and a deep copy is created on demand when hierarchically deep data within the reference object is accessed.