OOC-PString-Defines.h

#define $(obj,method) obj->method(obj)
#define $$(obj,method,args) obj->method(obj,args)

OOC-PString-Example.c

PString * str = initializePString();
str.setValue(str, "a value");
printf("string: %s", str.value(str));
str.destroy(str);

OOC-PString-WithMacros.c

PString *str = initializePString();
$$(str, setValue, "a value");
printf("string: %s", $(str, value));
$(str, destroy);

OOC-PString1.c

PString * initializePString() {
  PString *str=(PString*)malloc(sizeof(PString));
  str->chars = (char *)malloc(sizeof(char) * 1);
  str->chars[0] = '';
  str->length = &length;
  str->characterAtIndex = &characterAtIndex;
  str->value = &value;
  str->setValue = &setValue;
  str->destroy = &destroy;
  return str;
}

OOC-PString1.h

typedef struct pstring_t {
  /*
   instance variables
   */
  char * chars;
  
  /*
   instance methods
   */
  int (* length)(struct pstring_t *);
  char (* characterAtIndex)(struct pstring_t *, int);
  char * (* value)(struct pstring_t *);
  void (* setValue)(struct pstring_t *, char *);
  void (* destroy)(struct pstring_t *);
} PString;

OOC-PString2.c

int length(PString * self) {
  return strlen(self->chars);
}

char characterAtIndex(PString * self, int i) {
  return self->chars[i];
}

char * value(PString * self) {
  return self->chars;
}

void setValue(PString * self, char * chars) {
  free(self->chars);
  self->chars = (char *)malloc(sizeof(char) * (strlen(chars) + 1));
  strcpy(self->chars, chars);
}

void destroy(PString * self) {
  free(self->chars);
  free(self);
}

OOC-PString2.h

PString * initializePString();
int length(PString * self);
char characterAtIndex(PString * self, int i);
char * value (PString * self);
void setValue(PString * self, char * chars);
void destroy(PString * self);