/*
 *        dependcy.h
 *        Dependency class
 *        AYM 2000-04-09
 */


/* This class, along with the Serial_num class, allow one to
   express a relationship of dependency (think makefiles)
   between two objects. For the sake of discussion, let's assume
   that class Target depends on class Source.

   Make Source use a Serial_num object and make it call
   Serial_num::bump() whenever it changes. Make Target use a
   Dependency object. The Dependency object should be
   constructed with a pointer to the Serial_num member of Source.

   In all public methods of Target, start by checking whether
   Source has been modified while we were out by calling
   Dependency::outdated(). If the latter returns true, Target
   shall update itself based on the new state of Source and then
   call Dependency::update(). */


#ifndef YH_DEPENDCY                /* DO NOT INSERT ANYTHING BEFORE THIS LINE */
#define YH_DEPENDCY


class Serial_num;                // Defined in serialnum.h
typedef unsigned long serial_num_t;        // Copied from serialnum.h


class Dependency
{
    public: Dependency(Serial_num * sn);
    bool outdated();
    void update();

      private: Serial_num * serial_num;
    serial_num_t token;
    bool token_valid;
};


#endif /* DO NOT ADD ANYTHING AFTER THIS LINE */