Callback cleaner: context can be taken from timer

src/timer.cpp

@@ -9,12 +9,12 @@ std::mutex sc::timer::mutex;
 
 void sc::timer::callback(union sigval sv) {
     timer* self = reinterpret_cast<timer*>(sv.sival_ptr);
-    self->_expired_func(self, self->_context);
+    self->_expired_func(self);
 }
 
-sc::timer::timer(void(*expired_func)(timer*, void*),
+sc::timer::timer(double time,
-                 double time,
                  bool repeat,
+                 void(*expired_func)(timer*),
                  void* context)
     : _id {}, _time {time}, _repeat {repeat},
       _expired_func {expired_func}, _context {context}

src/timer.hpp

@@ -14,21 +14,22 @@ namespace sc {
         uint64_t _id {};
         double _time {};
         bool _repeat {};
-        void (*_expired_func)(timer* self, void* context);
+        void (*_expired_func)(timer* self);
         void* _context {};
 
         static void callback(union sigval);
 
         public:
-            timer(void(*expired_func)(timer*, void*),
+            timer(double time,
-                  double time,
                   bool repeat,
-                  void* context);
+                  void(*expired_func)(timer*),
+                  void* context = nullptr);
             ~timer();
 
             uint64_t id() const { return _id; }
             double time() const { return _time; }
             bool repeat() const { return _repeat; }
+            void* context() const { return _context; }
 
             bool is_armed() const;
             void time_left(struct itimerspec& cur_value) const;