Joining a plurality of type hierarchies in an object oriented programming language without inheriting from a base class and without modification to the type hiearchies

• US 6,142,684 A
• Filed: 04/03/1997
• Issued: 11/07/2000
• Est. Priority Date: 04/03/1997
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc., Hewlett-Packard Company (HP Inc.), Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Kirshenbaum, Evan R., Moore, Keith E.
• Primary Examiner(s): Hafiz, Tariq R.
• Assistant Examiner(s): INGBERG, TODD D
• Application Number:
  US08/826,540
• Time in Patent Office: 1,314 Days
• Field of Search: 395/703, 395/708, 395/707
• US Class Current: 717/143
• CPC Class Codes: G06F 9/4492 Inheritance

Abstract

A system and method using a computer for joining a plurality of hierarchies of types is described. Each type in each type hierarchy includes a template for objects. At least one reference class is defined as computer-readable instructions stored in a memory of a computer for defining a class and includes a discriminator which can refer to instances of at least one such type within one of the type hierarchies and including, for each type hierarchy, an initialization function which takes as an argument a reference to an instance of any of the types in the type hierarchy. The initialization function included for each type hierarchy is performed by loading the discriminator with the argument of the initialization function.

Claims

1. A system for creating a pretense of joining a plurality of type hierarchies in a single hierarchy, the system comprising a computer including a processor, a memory and input/output facilities, each type in each type hierarchy having a template describing objects that are instances of the type, comprising:

at least one reference class to refer to the type hierarchies as if the referred type hierarchies were inherited from a common base class such that separate and unrelated ones of the type hierarchies can be joined together without modifying the type hierarchies, wherein the referred type hierarchies are not physically modified to refer to the common base class wherein the reference class further includes

a discriminator which can refer to instances of at least one such type within one of the type hierarchies, wherein the discriminator discriminates between the type hierarchies; and

for each type hierarchy, an initialization function which takes as an argument a reference to an instance of any of the types in the type hierarchy, wherein the initialization function is performed by loading the discriminator with the argument; and

the initialization function is performed by loading the discriminator with the argument; and

the processor being operative to read the reference class and responsive to the initialization function included for each type hierarchy to load the discriminator with the argument of the initialization function.

2. A system according to claim 1, wherein the discriminator comprises a state indicia and a reference indicia, the processor further comprising:

means for setting the state indicia to uniquely identify the type hierarchy of the instance referred to by the discriminator; and

means for loading the reference indicia with an address for the instance of the corresponding uniquely identified type hierarchy.

3. A system according to claim 2, wherein the state indicia is an enumerated data type including one value corresponding to each type hierarchy and the reference indicia is a pointer union including one pointer corresponding to each type hierarchy.

4. A system according to claim 1, the processor further comprising means for restricting the initialization functions of one such reference class to accepting references to objects that are to be treated as constant.

5. A system according to claim 4, the processor further comprising:

means for defining the initialization functions of a further such reference class accepting references to instances of substantially each such type within the type hierarchies of the one such reference class; and

means for providing a conversion function to the one such reference class from the further such reference class.

6. A system according to claim 1, the processor further comprising means for defining the reference class to present functions of an interface of a base class of one of the type hierarchies.

7. A system according to claim 1, the processor further comprising means for defining the reference class to present functions of an interface of a fictitious class.

8. A system according to claim 1, wherein at least one of the type hierarchies includes a built-in data type.

9. A method of using a computer for creating a pretense of joining a plurality of type hierarchies in a single hierarchy, each type in each type hierarchy comprising a template describing objects that are instances of the type, comprising the steps of:

defining at least one reference class to refer to the type hierarchies as if the referred type hierarchies were inherited from a common base class in a single hierarchy such that separate and unrelated ones of the type hierarchies can be joined together without modifying the type hierarchies, wherein the referred type hierarchies are not physically modified to refer to the common base class wherein the reference class further includes

a discriminator which can refer to instances of at least one such type within one of the type hierarchies, wherein the discriminator discriminates between the type hierarchies,

for each type hierarchy, an initialization function which takes as an argument a reference to an instance of any of the types in the type hierarchy, wherein the initialization function is performed by loading the discriminator with the argument; and

performing the initialization function included for each type hierarchy by loading the discriminator with the argument of the initialization function.

10. A method according to claim 9, further comprising the step of implementing at least one function of the at least one reference class through use of the instance of the type hierarchy referred to by one such discriminator.

11. A method according to claim 10, wherein the use of the instance of the type hierarchy comprises the step of invoking a function having a same name as the function being implemented.

12. A method according to claim 9, wherein at least one of the initialization functions is a constructor function.

13. A method according to claim 9, wherein at least one of the initialization functions is an assignment operation.

14. A method according to claim 9, wherein the discriminator comprises a state indicia and a reference indicia, the method further comprising the steps of:

setting the state indicia to uniquely identify the type hierarchy of the instance referred to by the discriminator; and

loading the reference indicia with an address for the instance of the corresponding uniquely identified type hierarchy.

15. A method according to claim 14, wherein the state indicia is an enumerated data type including one value corresponding to each type hierarchy and the reference indicia is a pointer union including one pointer corresponding to each type hierarchy, the step of setting the state indicia further comprising the step of selecting the value of the enumerated data type corresponding to the type hierarchy and the step of loading the reference indicia further comprising the step of setting the corresponding pointer of the pointer union to the address for the type hierarchy instance.

16. A method according to claim 9, further comprising the step of restricting the initialization functions of one such reference class to accepting references to objects that are to be treated as constant.

17. A method according to claim 16, further comprising the steps of:

defining the initialization functions of a further such reference class accepting references to instances of substantially each such type within the type hierarchies of the one such reference class; and

providing a conversion function to the one such reference class from the further such reference class.

18. A method according to claim 17, further comprising the steps of:

defining the one such reference class to present functions of an identified interface of a base class of one of the type hierarchies, the functions being declared as restricted to such functions appropriate to constant instances; and

defining the one such further reference class to present functions of the identified interface of the base class, the functions being declared as restricted to such functions appropriate to nonconstant instances.

19. A method according to claim 17, further comprising the steps of:

defining the one such reference class to present functions of an interface of a fictitious class, the functions being declared as restricted to such functions appropriate to constant instances; and

defining the one such further reference class to present functions of an interface of the fictitious class, the functions being declared as restricted to such functions appropriate to nonconstant instances.

20. A method according to claim 17, further comprising the step of deriving the further such reference class from the one such reference class.

21. A method according to claim 16, further comprising the step of implementing at least one function of the reference class through use of the instance of the type hierarchy referred to by one such discriminator, the use of the instance being restricted to operations appropriate to objects that are to be treated as constant.

22. A method according to claim 9, further comprising the step of defining the reference class to present functions of an interface of a base class of one of the type hierarchies.

23. A method according to claim 9, further comprising the step of defining the reference class to present functions of an interface of a fictitious class.

24. A method according to claim 9, wherein at least one of the type hierarchies includes a built-in data type.

25. A computer-readable storage medium for encoding program code for creating a pretense of joining a plurality of type hierarchies in a single hierarchy, each type in each type hierarchy comprising a template describing objects that are instances of the type, comprising:

instructions that define at least one reference class to refer to the type hierarchies as if the referred type hierarchies were inherited from a common base class in a single hierarchy such that separate and unrelated ones of the type hierarchies can be joined together without modifying the type hierarchies, wherein the referred type hierarchies are not physically modified to refer to the common base class wherein the reference class further includes

a discriminator which can refer to instances of at least one such type within one of the type hierarchies, wherein the discriminator discriminates between the type hierarchies,

for each type hierarchy, an initialization function which takes as an argument a reference to an instance of any of the types in the type hierarchy, wherein the initialization function is performed by loading the discriminator with the argument; and

instructions that perform the initialization function included for each type hierarchy by loading the discriminator with the argument of the initialization function.

26. A storage medium according to claim 25, further comprising instructions for implementing at least one function of the at least one reference class through use of the instance of the type hierarchy referred to by one such discriminator.

27. A storage medium according to claim 25, wherein the discriminator comprises a state indicia and a reference indicia, the storage medium further comprising:

instructions for setting the state indicia to uniquely identify the type hierarchy of the instance referred to by the discriminator; and

instructions for loading the reference indicia with an address for the instance of the corresponding uniquely identified type hierarchy.

28. A storage medium according to claim 25, further comprising instructions for restricting the initialization functions of one such reference class to accepting references to objects that are to be treated as constant.

29. A storage medium according to claim 28, further comprising:

instructions for defining the initialization functions of a further such reference class accepting references to instances of substantially each such type within the type hierarchies of the one such reference class; and

instructions for providing a conversion function to the one such reference class from the further such reference class.

30. A storage medium according to claim 29, further comprising:

instructions for defining the one such reference class to present functions of an identified interface of a base class of one of the type hierarchies, the functions being declared as restricted to such functions appropriate to constant instances; and

instructions for defining the one such further reference class to present functions of the identified interface of the base class, the functions being declared as restricted to such functions appropriate to nonconstant instances.

31. A storage medium according to claim 29, further comprising:

instructions for defining the one such reference class to present functions of an interface of a fictitious class, the functions being declared as restricted to such functions appropriate to constant instances; and

instructions for defining the one such further reference class to present functions of an interface of the fictitious class, the functions being declared as restricted to such functions appropriate to nonconstant instances.