/* File: CExamples/OO_pgm_in_C_new/stack.h */

/* This is the abstract data object; initialize by calling new_stack
                                     remove by calling delete_stack */
typedef struct stackstruct
  { void *objptr; /* address of data structure */

    /* abstract methods;
       the actual data structure of the stack is accessed as self->objptr
       In C++ self is the keyword this; self is from Smalltalk */
    int (*is_empty)(struct stackstruct* self); /* returns 0 if *self is empty */
    void(*push)    (int, struct stackstruct* self);
    int (*pop)     (struct stackstruct* self);

    /* object manipulation; see also new_stack, delete_stack below */
    struct stackstruct* (*clone) (struct stackstruct* self); /* make a copy */
  } stack,  *stackptr;
  
/* a generic function */
extern void print_stack(stack s);

/* the following functions are specific to the data structure used:
   therefore, there can only be one data structure used by
   a program, which is a restriction.  One could overcome
   this restriction by placing pointers to new and delete inside
   struct stackstruct; however, in the current model the
   function main() is also generic via the linking mechanism.
   for more on these different forms of genericity, see:
   http://www.math.ncsu.edu/~kaltofen/bibliography/index.html#EKM96
*/
extern stackptr new_stack(void);
extern void delete_stack(stackptr);