泛化传递给 boost::bind 的参数

Question

我正在尝试编写一个使用 boost::bind 的通用结构 MyCounter 。我想要做的是编写MyCounter 这样通过更改其模板参数类型，我可以绑定到不同的方法。我的印象是，如果我将MyThread::send 之类的东西作为模板参数传递，我将能够直接在bind() 中使用它。显然我错了。你能帮我解决一些问题吗？谢谢

#include <boost/bind.hpp>
#include <boost/function.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
#include <vector>
#include <utility>

struct MyThread //simplified
{
    void send1()
    {
        std::cout << "In Send1\n";
    }
    void send2()
    {
        std::cout << "In Send2\n";
    }
};

struct Job //ignore me
{
    Job(const unsigned int interval)
        : _tChk(0)
        , _tInterval(interval)
    {}

    void operator()(unsigned long nowSec)
    {
        if (nowSec > _tChk)
        {
            _functor();
            _tChk += nowSec + _tInterval;
        }
    }

private:
    unsigned long  _tChk;
    const unsigned int  _tInterval;

protected:
    boost::function<void()> _functor;
};

struct JobInvoker //ignore me
{
    typedef boost::shared_ptr<Job> JobPtr;
    JobInvoker(MyThread &myThread)
        : _myThread(myThread)
    {}

    template<typename JOB>
    void addJob(const unsigned int interval)
    {
        JobPtr job = boost::make_shared<JOB>(interval, _myThread);
        _jobs.push_back(job);
    }

    void operator() (JobPtr job)
    {
        (*job)(_now.tv_sec);
    }

    void invoke(timeval now)
    {
        _now = now;
        std::for_each(_jobs.begin(), _jobs.end(), *this);
    }

    timeval _now;
    std::vector<JobPtr> _jobs;
    MyThread &_myThread;
};

//my struggle
template<typename F>
struct MyCounter : public Job
{
    MyCounter(const unsigned int interval, MyThread &myThread)
    : Job(interval)
    {
        _functor = boost::bind(&F, &myThread); //<-- Error
    }
};

int main()
{
  MyThread t;
  JobInvoker jobInvoker(t);
  jobInvoker.addJob<MyCounter<MyThread::send1> >(2); //<-- Error
  jobInvoker.addJob<MyCounter<MyThread::send2> >(2); //<-- Error
  timeval now;//...
  jobInvoker.invoke(timeval now)
  return 0;
}

更新： 编译： g++ boost_f.cpp -lboost_system

我们得到以下错误：

boost_f.cpp: In constructor ‘MyCounter<F>::MyCounter(unsigned int, MyThread&)’:
boost_f.cpp:81:34: error: expected primary-expression before ‘,’ token
         _functor = boost::bind(&F, &myThread); //<-- Error
                                  ^
boost_f.cpp: In function ‘int main()’:
boost_f.cpp:89:46: error: type/value mismatch at argument 1 in template parameter list for ‘template<class F> struct MyCounter’
   jobInvoker.addJob<MyCounter<MyThread::send1> >(2); //<-- Error
                                              ^
boost_f.cpp:89:46: error:   expected a type, got ‘MyThread::send1’
boost_f.cpp:89:51: error: no matching function for call to ‘JobInvoker::addJob(int)’
   jobInvoker.addJob<MyCounter<MyThread::send1> >(2); //<-- Error
                                                   ^
boost_f.cpp:89:51: note: candidate is:
boost_f.cpp:52:10: note: template<class JOB> void JobInvoker::addJob(unsigned int)
     void addJob(const unsigned int interval)
          ^
boost_f.cpp:52:10: note:   template argument deduction/substitution failed:
boost_f.cpp:89:51: error: template argument 1 is invalid
   jobInvoker.addJob<MyCounter<MyThread::send1> >(2); //<-- Error
                                                   ^
boost_f.cpp:90:46: error: type/value mismatch at argument 1 in template parameter list for ‘template<class F> struct MyCounter’
   jobInvoker.addJob<MyCounter<MyThread::send2> >(2); //<-- Error
                                              ^
boost_f.cpp:90:46: error:   expected a type, got ‘MyThread::send2’
boost_f.cpp:90:51: error: no matching function for call to ‘JobInvoker::addJob(int)’
   jobInvoker.addJob<MyCounter<MyThread::send2> >(2); //<-- Error
                                                   ^
boost_f.cpp:90:51: note: candidate is:
boost_f.cpp:52:10: note: template<class JOB> void JobInvoker::addJob(unsigned int)
     void addJob(const unsigned int interval)
          ^
boost_f.cpp:52:10: note:   template argument deduction/substitution failed:
boost_f.cpp:90:51: error: template argument 1 is invalid
   jobInvoker.addJob<MyCounter<MyThread::send2> >(2); //<-- Error
                                                   ^
boost_f.cpp:92:29: error: expected primary-expression before ‘now’
   jobInvoker.invoke(timeval now)

Answer 1

正如错误所说，成员函数不是类型，因此它不能用于模板类型参数。

相反，您需要使用非类型参数：

template<void(MyThread::*F)()>
struct MyCounter : public Job
{   
    MyCounter(const unsigned int interval, MyThread &myThread)
    : Job(interval)
    {
        _functor = boost::bind(F, &myThread);
    }
};

Live Example

请注意，我将F 设为指向MyThread 的成员函数的指针，而不是typename。