Abstract:
An object-oriented technology is provided which is capable of operating interpretively to allow prompt and easy prototyping and debugging using a compiled class library, and which is also capable of operating after compilation, thereby providing excellent performance. A software facility allows direct access to class attributes and direct invocation of class methods defined in pre-compiled classes in a class library in an interpretive mode. When this facility is used with or embedded within an application development environment, it allows an application builder to interactively build prototypes as well as production quality applications rapidly. When the facility is integrated with an object-oriented database, it allows interactive query and data manipulation using pre-complied classes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 07/621,748, filed Nov. 30, 1990, now abandoned. 
    
    
     BACKGROUND 
     This invention pertains to object oriented technology, and particularly to a novel object-oriented system which allows direct access to attributes and direct invocation of methods defined in compiled classes in an interpretive mode. 
     Object-oriented technology is beginning to enjoy wide-spread popularity in recent years. When using object-oriented technology to build applications, a user must first build the underlying classes. These classes are then used to develop applications in a similar way that integrated circuits are used to build electronic devices. To build these classes and applications, object-oriented languages like Smalltalk and C++ are commonly used. These two languages are unlike each other in one very important aspect. Smalltalk is a fully interpretive language that allows rapid prototyping of classes and applications, but at the expense of performance. On the other hand, programs written in C++ must be compiled and linked before they can be executed. This allows for fast program execution but makes C++ unsuitable for rapid prototyping and debugging. 
     Given the relative complexity of many object-oriented packages, prototyping and debugging are not simple tasks, but rather involve a considerable amount of effort and a number of iterations in order to perfect the software product. Accordingly, the inability of object-oriented languages to operate in an interpretive fashion makes prototyping and debugging utilizing such non-interpretive software extremely difficult and time-consuming. Conversely, object-oriented technologies which operate in an interpretive manner, but which cannot be compiled, introduces severe performance penalties which utilizing such interpretive object-oriented technologies. 
     An objective of this invention is to provide a system and method for rapid prototyping of object-oriented applications which can be deployed in a production environment. Rapid prototyping requires an interpreter so that the source code of an application can be executed immediately without requiring compilation. Heretofore, applications executed through an interpreter have unacceptable performance and so cannot be used in a production environment. In the prior art, to have acceptable performance, applications must be compiled first into object code. This code is then deployed in a production environment for execution. But this sacrifices rapid prototyping as the compilation which must be done first is an involved and time-consuming process. Therefore, in accordance with the teachings of this invention, rapid prototyping and yet adequate performance for production deployment is provided by the novel concept in which an application is partially interpreted and partially compiled. With object-oriented technology, classes are commercially available for building applications. These classes are building blocks which are available in pre-compiled form to allow developers to create complex applications without the need to create the classes themselves. By providing a system and a method to &#34;assemble&#34; these pre-compiled classes interpretively to build applications, this invention provides rapid prototyping of source code applications that accesses these classes by interpretively executing the source code during prototyping and debugging, while allowing these source code applications to be deployed in a production environment, since these classes are already compiled and therefore offer acceptable performance. 
     In accordance with this invention, direct access to attributes and direct invocation of methods defined in the compiled classes is performed in an interpretive mode. When this facility is used with or embedded within an application development environment, it allows an application builder to interactively build prototypes as well as production quality applications rapidly. When the facility is integrated with an object-oriented database, it allows interactive query and data manipulation using compiled classes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1 through 4 are flow charts depicting one embodiment of this invention. 
    
    
     DETAILED DESCRIPTION 
     The following detailed description describes on embodiment of this invention which is particularly well suited for use in the object-oriented language known as C++. However, it is to be understood that the teachings of this invention are equally applicable to any object-oriented technology, including languages other than C++. 
     DT=Dispatch tables 
     OMP=Object Manipulation Functions 
     ID=Interpretive dispatcher 
     OEF=Object Entry Functions 
     The embodiment of this invention will now be described with reference to FIGS. 1 and 2 which depict the operation of and interaction between the following modules: 
     a. The Class Scanner. Class Scanner 101 is used to determine the attributes of classes contained in header files 102 of a compiled class library 122. Class Scanner 101 extracts class information 103 from the header files contained in class library 122 in order to have ready access to sufficient information to understand the nature of each class. Class Scanner 101 is, preferably, run only once (unless the library changes), with the extracted information being stored for ready access without the need to run Class Scanner 101 again. In the event class library 122 is altered, Class Scanner 101 can either scan the entire class library again to extract information pertaining to each class, or can be used to extract information only pertaining to the new or altered classes, thus increasing the speed of operation. Besides extracting class information, Class Scanner 101 also generates various Object Manipulation Functions (OMF) 112 (FIG. 3) for each scanned class. These functions perform various operations on objects such as invoking their methods, accessing their attributes, performing object copy, and the like. 
     b. The Class Selector. Class Selector 104 is a mechanism to allow a user to choose classes from those available on the class information file provided by Class Scanner 101. Only objects from these selected classes are then accessible by Object Handler 130. 
     c. The Object Handler. Object Handler 130. provides a convenient mechanism for utilizing class information 103 pertaining to each class, which information has been extracted by Class Scanner 101. Object Handler 130 thus allows a user to gain access to an object in a convenient manner. 
     d. The Interpretive Dispatcher. Interpretive Dispatcher 120 manipulates an object, using the access to the object which is established by Object Handler 104. Interpretive Dispatcher 120 allows immediate execution of object-oriented source code by recognizing and executing the object-oriented code syntax. In accordance with the teachings of this invention, since Class Scanner 101 has extracted information pertaining to each class automatically, Interpretive Dispatcher 120 avoids the need to declare which header files will be used and their attributes, which provides a distinct advantage over prior art object-oriented compilers. 
     A more detailed description of one embodiment of these modules is now provided. 
     The Class Scanner 
     FIGS. 3 and 4 form a flow chart of one embodiment of Class Scanner 101. In order to allow access to classes, the knowledge of the structure of these classes must be made known. In &#34;C++&#34;, all class definitions are available and can be found in .h files, which together with the compiled classes form the class library 122. This library could be developed by the user or obtained from external sources. In Step 107, Class Scanner 101 first combines .h files 102 in compiled class library 122 into a single VIRAGOTEMP3-.CXX file 108, which is then preprocessed in Step 109 to create File.scanh 110. File.scanh 110 is then parsed in step 111 in order to obtain and store in Class Information file 103 the following information about each class: 
     a. Class name. 
     b. Class attributes (e.g. public, protected &amp; private). 
     c. It&#39;s superclass. (or superclasses in case of multiple inheritance). 
     d. It&#39;s Class method (e.g. virtual, public, protected, and private). 
     e. The argument types of these Class methods. 
     f. Whether the class is an abstract class. 
     Besides this information, Class Scanner 101 also stores information about typedefs and global variable declarations. 
     Class Scanner 101 also generates through Step 111 C++ source code to form various Object Manipulation Functions (OMF) 112 to perform desired operations on the scanned classes. For example, the following Object Manipulation Functions are created for each class scanned: 
     a. a function to invoke the class method (including static method). 
     b. a function to access each class attribute. 
     c. a function to perform object copy. 
     d. a function to perform casting of objects. 
     from base class to derived class. 
     from derived class to base class. 
     e. a function to do class assignment. 
     f. a function to allocate multi-dimension object arrays. 
     g. a function to return the size of the class. 
     Naturally, it is to be understood that not all applications will need each of these functions, or additional functions maybe useful in certain applications. The selection of functions, including functions not described in this example, is apparent to those of ordinary skill in the art in light of the teaching of this invention. Furthermore, for embodiments of this invention which utilize other than C++ object oriented code, functions may be used other than the examples given above. 
     Annex I, below, provides examples of code generated for each of these Object Manipulation Functions 112 of Class Scanner 101. 
     Besides parsing File.scanh, step 111 also executes the create --  exp --  ifile to create the expand --  ifile.h file 112. 
     In addition, Class Scanner 101 also generates code for a function that creates a table of sizes to store the size of a class returned by the function g. above. 
     After the C++ source code for the above Object Manipulation Functions 112 have been generated and the expand --  ifile.h file have been created, they are translated to C source code by a C++ translator such as the Cfront translator available from AT&amp;T. The resulting translated OMF source code 113 is then patched by patch program 114 provided in accordance with the teachings of this invention. Patched code 115 is then compiled by a C compiler to form the Object Manipulation Functions (OMF) library 116, which forms part of Object Handler 103, as depicted in FIG. 2. 
     When an object-oriented function is executed, it normally returns a value which is either a class object, a type of pointer, or a fundamental type, depending upon the operation of the function. However, for the above Object Manipulation Functions 112, a descriptor of the return value rather than the value itself is returned. The descriptor has a structure defined as: 
     
         ______________________________________    struct descriptor {      int type;      int flag;      union {      void *return.sub.-- value;      int *Vint;      . .      all fundamental types.      . .      class1 *Vclass1;      class1 **V1class1;      class1 ***V2class1;      class2 *Vclass2;      class2 **V1class2;      class2 ***V2class2;      . .      . .      };______________________________________ 
    
     In the above descriptor structure, &#34;type&#34; describes the type specification of the return value, and &#34;flag&#34; is used to indicate how the descriptor is to be freed after use. 
     As shown in the above descriptor structure, each class includes one line for each level of indirection; the above descriptor structure example has three levels of indirection for class 1 and class 2. 
     For the structure defined above, each scanned class can have a pointer to an object, a pointer to pointer to an object, and a pointer to pointer to pointer to an object. Should more indirection be needed, the union structure can be extended. For example, when an int is to be returned, the return --  value in the descriptor structure is the address of that int. When an object is to be returned, the return --  value is the address of that object. When a pointer to an object is to be returned, the return --  value is the address of the object address pointer. 
     Appendix I are C and C++ source code listings for the following files which serve as one embodiment of Class Scanner 101 suitable for use with the C++ object-oriented language. 
     SCANNER/makefile 
     SCANNER/scanner --  lex.lex 
     SCANNER/scanner --  parser.y 
     SCANNER/scanner.h 
     SCANNER/scanner.c 
     SCANNER/scanner --  extern.h 
     SCANNER/symbol --  entry.h 
     SCANNER/CREATE --  EXP --  IFILE/makefile 
     SCANNER/CREATE --  EXP --  IFILE/create --  exp --  ifile.lex 
     SCANNER/CREATE --  EXP --  IFILE/create --  exp --  ifile.c 
     PATCH/makefile 
     PATCH/patch.c 
     PATCH/patch.h 
     PATCH/patch.lex 
     The Class Selector 
     Class Selector 104 (FIG. 1) allows a user to select only those classes whose objects the user wishes Object Handler 130 to access. The Class Information of these selected classes is then used as input to generate the C++ source code of the dispatch tables (DT) to the Object Manipulation Functions (OMF) 105. This C++ source code is then translated to C source code, which is then compiled and stored as DT to OMF library 106, one of the three libraries of Object Handler 130. Dispatch tables are well known in the art and thus specific code used to implement a suitable dispatch table is not discussed. 
     Appendix II are C and C++ source code listings for the following files which serve as one embodiment of Class Selector 104 suitable for use with the C++ object-oriented language. 
     CLASS --  SELECTOR/makefile 
     CLASS --  SELECTOR/class --  selector.cxx 
     The Object Handler 
     Object Handler 130 includes Object Entry Functions (OEF) library 118, DT to OMF library 106, and OMF library 116. OEF Library 118 is obtained by translating using a C++ translator and then compiling using a C compiler the C++ source code of the Object Entry Functions 117 written in accordance with this invention. Object Handler 130 is the interface to compiled class library 122. Interpretive Dispatcher 120 uses Object Handler 130 to gain access to attributes and methods of user-defined compiled classes. There are several entry points to Object Handler 130. These entry points, which constitute Object Entry Functions (OEF) library 118, call the corresponding generated Object Manipulation Functions of OMF library 116 through dispatch tables of DT to OMF library 106, which in turn make calls to compiled class library 122. 
     The declaration of the entry points are: 
     
         ______________________________________a.       struct descriptor *      call.sub.-- method(char *classname, char        *methodname,        void *objectptr,        struct descriptor *argument.sub.-- array[],        int argument.sub.-- count;b.       struct descriptor *      call.sub.-- getattr(char *classname,        char *attributename, void        *objectptr);c.       void call.sub.-- copy(struct descriptor *from);d.       void call.sub.-- cast(char *fromclass, char *toclass,      void *fromclassobjectptr);e.       void call.sub.-- assign(void *fromobjectptr,      void *toobjectptr,      char *classname);f.       struct descriptor *      call.sub.-- array(char *classname,        int sub1, int sub2 ...);g.       int get.sub.-- sizeof(char *classname);______________________________________ 
    
     In function call --  method (function &#34;a&#34;), the arguments in the array of descriptor may not be the exact match of a class method. In this case, integral promotions, integral conversions, arithmetic conversions, pointer conversions, and/or reference conversions had to be performed on the argument list to make it an exact match before dispatching the argument list to the functions generated by Class Scanner 101. 
     Appendix III are C and C++ source code listings for the following files which serve as one embodiment of Object Handler 130 suitable for use with the C++ object-oriented language. 
     ENTRY --  FUNCTIONS/makefile 
     ENTRY --  FUNCTIONS/classinfo.h 
     ENTRY --  FUNCTIONS/classinfo.cxx 
     ENTRY --  FUNCTIONS/entry --  functions.cxx 
     ENTRY --  FUNCTIONS/error --  code.h 
     Object Handler 130 also includes object manipulation functions contained in library 116, and dispatch tables to object manipulation functions, contained in DT to OMF library 106. The object manipulation functions are generated by Class Scanner 101 while the Dispatch Tables to Object Manipulation Functions are generated by Class Selector 104, as described above. 
     The Interpretive Dispatcher 
     Interpretive Dispatcher 120 accepts C++ statements as char * and converts it into tokens of immediate codes. These codes are then evaluated. Should access to classes be needed, Interpretive Dispatcher 120 calls the respective routines in Object Handler 130 to do the job. Interpretive Dispatcher 120 is shown in FIG. 2 as a library. This library is obtained by translating using a C++ Translator and then compiling using a C compiler the source code of the Interpretive Dispatcher written in accordance with this invention. 
     The format to be used by another program to make a call to Interpretive Dispatcher 120 is, for example, as follows: 
     dml(char *statements); where &#34;statements&#34; is a string of program code which is to be interpreted by Interpretive Dispatcher 120. 
     For example, for the class below: 
     
         ______________________________________class Customer { char name[30]; float amount; static customer* lookup(char *customername); void setamount(float amt) { amount = amt;} }______________________________________ 
    
     to set the amount of Customer &#34;foobar&#34; to 1234.56, the following call is made to Interpretive Dispatcher 120: 
     dml(&#34;Customer *a=Customer::lookup( &#34;foobar &#34;); a→setamount(1234.56);&#34;); 
     As Interpretive Dispatcher 120 dynamically accepts any string of statements and executes them, Interpretive Dispatcher 120 together with Object Handler 130 can conveniently be used with or embedded in object-oriented tools to interactively develop applications. Dispatcher 120 can also be integrated with an object-oriented database for interactive query or data manipulation using compiled classes. This is convenient, for example, for use with screen builders, object-oriented databases (including allowing a client on a network to send a string of statements, for example, over a communication network to a server for execution), and for use in connection with report generators. Interpreters are well known in the art and thus specific code used to implement a suitable interpreter will not be discussed. 
     Finally, in order to use this invention to develop applications, the following libraries are linked together into a single body of executable code 131: 
     Tools or Database Library 121 
     Interpretive Dispatcher (ID) Library 120 
     Object Entry Function (OEF) Library 118 
     Dispatch Table to Object Manipulation Functions (OT to OMF) Library 106 
     Object Manipulation Functions (OMF) Library 116 
     Class Library 122 
     This linking enables tools (including screen builders and report generators) or object-oriented databases 121 to have an interpretive object-oriented facility for on-line and interactive access of pre-compiled classes in the class library 122, i.e. classes which have been written using object-oriented source code and have been compiled into object code to form Class Library 122. 
     ANNEX I 
     The details of one embodiment of the generated codes for each of the class scanner Object Manipulation Functions 112 described above are as follows: 
     a. Function to invoke each class method 
     Before method invocation, Object Handler 130 has already created a global object pointer (void *objectptr) pointing to the object instance, a global array of descriptors (struct descriptor *global --  argument) which describes the arguments of the method, and a count of the number of descriptors. 
     Thus, to generate code for a function to invoke, for example, a class method of class0, i.e.: 
     class3 a --  method (int, class1, class2*) 
     where the method name is a --  method, the return value is a class object of class3, and the arguments are int, class1, and pointer to class2 (class2*), the following code is generated: 
     
         ______________________________________class3 temp = objectptr →a.sub.-- method(  *(global.sub.-- argument [0]→Vint),  *(global.sub.-- argument [1]→Vclass1),  *(global.sub.-- argument [2]→V1class2));______________________________________ 
    
     If the method is a static method, then the following code is generated: 
     
         ______________________________________class3 temp = class0::a.sub.-- method(  *(global.sub.-- argument [0]→Vint),  *(global.sub.-- argument [1]→Vclass1),  *(global.sub.-- argument [2]→V1class2));______________________________________ 
    
     A descriptor of temp should be built and returned. However, because temp is a local variable, it will be destructed when the function exits out of its local scope. To prevent temp from being destructed, temp could be declared static, but this will incur a huge memory overhead. To overcome these problems, in accordance with the teachings of this invention, the &#34;C&#34; output of the C++ translator is patched in order to change the code to behave as if temp is dynamically allocated and no destructor is called when the scope of temp ends. As well known to the art a C++ code, when translated, for example, by utilizing Cfront, a C++ translator available from AT&amp;T, becomes C code which can be compiled utilizing a standard C compiler. 
     For example, a C++ statement such as: 
     
         ______________________________________  class3 temp = objectptr→a.sub.-- method(    *(global.sub.-- arg [0]→Vint),    *(global.sub.-- arg [1]→Vclass1),    *(global.sub.-- arg [2]→V1class2));______________________________________ 
    
     would be translated by the C++ translator to something like the following C code: 
     
         ______________________________________ struct class3 .sub.---- 1temp; .sub.---- ct.sub.---- 6class3Fv ( &amp; .sub.---- 1temp ); .sub.---- 1temp = a.sub.-- method.sub.---- 6class0Fi6class1P6class2(  (struct class0*)object,  (*(global.sub.---- argument [0])→  .sub.---- O2.sub.---- 12value struct.Vint),  (*(global.sub.---- argument [1])→  .sub.---- O2.sub.---- 12value struct.Vclass1),  (*(global.sub.---- argument [2]→  .sub.---- O2.sub.---- 12value.sub.-- struct.Vclass2));.sub.---- dt.sub.---- 6class3Fv ( &amp;.sub.---- 1temp, 2);______________________________________ 
    
     Since temp is destroyed once it exits its scope, in accordance with the teachings of this invention a patch program has been written which when used scans the generated C code which has been generated by the C++ translator and which replaces all local variables (such as  --  1temp as shown in the above translated code with pre-defined global variables (such as glo --  temp). Glo --  temp is allocated sufficient memory space to hold what a --  method would return. In addition, the patch scan program also removes the destructor that was used to remove temp when it exits its scope. 
     The final patched C code is, for example: 
     
         ______________________________________  .sub.---- ct.sub.---- 6class3Fv ( &amp; glo .sub.-- temp );glo.sub.-- temp = a.sub.-- method.sub.---- 6class0Fi6class1P6class2(  (struct class0*)object,  (*(global.sub.---- argument [0])→  .sub.---- O2.sub.---- 12value struct.Vint),  (*(global.sub.---- argument [1])→  .sub.---- O2.sub.---- 12value struct.Vclass1),  (*(global.sub.---- argument [2])→  .sub.---- O2.sub.---- 12value.sub.-- struct.Vclass2));______________________________________ 
    
     Accordingly, in accordance with this aspect of the present invention, instead of a descriptor of local variable temp, a descriptor of global variable glo --  temp is built and returned. This return value, being a global variable, can be used even outside the scope where temp is declared. 
     b. Function to access class attributes 
     Before method invocation, Interpretive Dispatcher 120 has already created a global object pointer (void *objectptr) pointing to the object instance. This function simply return the descriptor of the attribute. For example, to return the attribute x of the following class: 
     
         ______________________________________    class y {    class1 x;    );______________________________________ 
    
     The following must be performed: 
     1. allocate space for a descriptor from dynamic memory with a memory allocation function called malloc as follows: 
     struct descriptor *a=(struct descriptor *)malloc (sizeof(struct descriptor)); 
     2. fill in the &#34;type&#34; and &#34;flag&#34; information into the descriptor. 
     3. generate the following &#34;C++&#34; code: 
     a→Vclass1=&amp;objectptr→x; 
     c. Function to perform object copy 
     This function can be used by Interpretive Dispatcher 120 to make a copy of an object instance. 
     This function contains the following generated code for a class x: 
     
         x temp=*((x *)objectptr); 
    
     Objectptr refers to the object instance where a copy is to be made. This objectptr is created by the Object Handler. The variable temp is again only local. The same patch to &#34;C&#34; code generated by the C++ translator is used, as explained previously with regard to the function to invoke class method. 
     d. Function to perform casting of objects 
     In the case where only a single inheritance is used, the function simply returns the original pointer values no matter whether the casting is from base classes to derived classes or from derived classes to base classes. 
     In the case of multiple inheritance and non-virtual base classes, the function generates casting code from base classes to derived classes and from derived classes to base classes. 
     For multiple inheritance involving virtual base classes, the function generates casting code only for casting from derived classes to base classes, because for standard &#34;C++&#34; casting of virtual base classes to derived classes is not supported by C++. 
     e. Function to do class assignment 
     This function contains generated code that takes two arguments of void *to, void *from of class x to perform: 
     
         *((x *)to)=*((x *)from); 
    
     f. Function to allocate multi-dimensional object arrays 
     This function contains generated code that allocates a descriptor as follows: 
     struct descriptor *a=(struct descriptor *)malloc (sizeof(struct descriptor)); 
     This generated code then fills in the type and flag information into the descriptor. This generated code also contains the following information, depending upon whether a one-dimensional or two-dimensional array is required: 
     a→V1x=new x [dimension1]; 
     
         or 
    
     
         a→V2x=new x [dimension1*dimension2]; 
    
     g. Function to get size of a class 
     This function contains the following generated code for class x: 
     
         sizeof(x) 
    
     and also code that stores the value of this size in a table of sizes which is also created by Class Scanner 104. 
     The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the appended claims. ##SPC1##