咋一看你能看明白吗？

咋一看你能看明白这是什么吗？来自<boost/signals/signal_template.hpp>

 1   template<
 2     typename R,
 3     BOOST_SIGNALS_TEMPLATE_PARMS
 4     BOOST_SIGNALS_COMMA_IF_NONZERO_ARGS
 5     typename Combiner,
 6     typename Group,
 7     typename GroupCompare,
 8     typename SlotFunction
 9   >
10   typename BOOST_SIGNALS_SIGNAL<
11              R, BOOST_SIGNALS_TEMPLATE_ARGS
12              BOOST_SIGNALS_COMMA_IF_NONZERO_ARGS
13              Combiner, Group, GroupCompare, SlotFunction>::result_type
14   BOOST_SIGNALS_SIGNAL<
15     R, BOOST_SIGNALS_TEMPLATE_ARGS
16     BOOST_SIGNALS_COMMA_IF_NONZERO_ARGS
17     Combiner, Group, GroupCompare, SlotFunction
18   >::operator()(BOOST_SIGNALS_PARMS)
19   {
20     // Notify the slot handling code that we are making a call
21     BOOST_SIGNALS_NAMESPACE::detail::call_notification notification(this->impl);
22 
23     // Construct a function object that will call the underlying slots
24     // with the given arguments.
25 #if BOOST_SIGNALS_NUM_ARGS == 0
26     BOOST_SIGNALS_ARGS_STRUCT_INST args;
27 #else
28     BOOST_SIGNALS_ARGS_STRUCT_INST args(BOOST_SIGNALS_ARGS);
29 #endif // BOOST_SIGNALS_NUM_ARGS > 0
30     call_bound_slot f(&args);
31 
32     typedef typename call_bound_slot::result_type call_result_type;
33     optional<call_result_type> cache;
34     // Let the combiner call the slots via a pair of input iterators
35     return combiner()(slot_call_iterator(notification.impl->slots_.begin(),
36                                          impl->slots_.end(), f, cache),
37                       slot_call_iterator(notification.impl->slots_.end(),
38                                          impl->slots_.end(), f, cache));
39   }

尤其后面35行的“return combiner()(slot_call_iterator(notification.impl->slots_.begin(), 36 impl->slots_.end(), f, cache), 37 slot_call_iterator(notification.impl->slots_.end(), 38 impl->slots_.end(), f, cache));”

我也是被这句话困扰了半个小时，后来追踪源码和自己理解终于明白了。

请看下面的简单模拟

 1 #include <boost/signals.hpp>
 2 #include <iostream>
 3 
 4 int testadd(int a, int b)
 5 {
 6     return a+b;
 7 }
 8 typedef int(*pfun)(int, int);
 9 pfun testfun()
10 {
11     return &testadd;
12 }
13 class testclass
14 {
15 private:
16     int a;
17     int b;
18 
19 public:
20     testclass() {}
21     testclass(int x, int y) : a(x), b(y) {}
22     int operator()()
23     {
24         return testfun()(a, b);
25     }
26 };
27 
28 int _tmain(int argc, _TCHAR* argv[])
29 {
30     testclass obj(3, 4);
31     std::cout << obj() << std::endl;
32 
33     return 0;
34 }

通过上面的代码你能看明白了吧，恩C++的语法方面就是比较复杂，一不留神就发现可能“很陌生”。

 

 

上面的问题的产生主要来自我对boost::Signals的学习

下面是书上的示例：

 1 #include <boost/signals.hpp>
 2 #include <iostream>
 3 
 4 void my_first_slot()
 5 {
 6     std::cout << "void my_first_slot()\n";
 7 }
 8 class my_second_slot
 9 {
10 public:
11     void operator()() const {    std::cout <<      "void my_second_slot::operator()() const\n";  }
12 };
13 
14 int _tmain(int argc, _TCHAR* argv[])
15 {
16     boost::signal<void ()> sig;
17     sig.connect(&my_first_slot);
18     sig.connect(my_second_slot());
19     std::cout << "Emitting a signal...\n";
20     sig();
21 
22     return 0;
23 }

20行的sig()引发的思考。

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

posted @ 2014-05-22 16:15  仙人球球  Views(1264)  Comments(0)  Edit  收藏  举报