c++ - 关于 Boost Signals2，没有名为 'apply' 的类模板

Question

我已经遵循了 Boost 教程“Passing Slots (Intermediate)”，引用文献 [1] 中的这封信，但我的代码出现了一个奇怪的错误，我无法破译或找不到任何帮助。我的代码如下:

[ 1 ] - http://www.boost.org/doc/libs/1_55_0/doc/html/signals2/tutorial.html#idp204830936

namespace GekkoFyre {
class TuiHangouts {
private:
    typedef boost::signals2::signal<void()> onRosterUpdate;
    typedef onRosterUpdate::slot_type onRosterUpdateSlotType;

    void logMsgs(std::string message, const xmppMsgType &msgType);
    void logMsgsDrawHistory();

    // Slots
    boost::signals2::connection doOnRosterUpdate(const onRosterUpdateSlotType &slot);
    onRosterUpdate rosterUpdate;
};
}

boost::signals2::connection GekkoFyre::TuiHangouts::doOnRosterUpdate(
        const GekkoFyre::TuiHangouts::onRosterUpdateSlotType &slot)
{
    return rosterUpdate.connect(slot);
}

具体问题在于:

void GekkoFyre::TuiHangouts::logMsgs(std::string message, const xmppMsgType &msgType)
{
    doOnRosterUpdate(&GekkoFyre::TuiHangouts::logMsgsDrawHistory);
}

我得到错误:

In file included from /usr/include/boost/function/detail/maybe_include.hpp:13:0,
                 from /usr/include/boost/function/detail/function_iterate.hpp:14,
                 from /usr/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47,
                 from /usr/include/boost/function.hpp:64,
                 from /usr/include/boost/signals2/signal.hpp:18,
                 from /usr/include/boost/signals2.hpp:19,
                 from /home/phobos/Programming/gecho/src/tui/chat.hpp:47,
                 from /home/phobos/Programming/gecho/src/tui/chat.cpp:35:
/usr/include/boost/function/function_template.hpp: In instantiation of 'void boost::function0<R>::assign_to(Functor) [with Functor = void (GekkoFyre::TuiHangouts::*)(); R = void]':
/usr/include/boost/function/function_template.hpp:722:7:   required from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value), int>::type) [with Functor = void (GekkoFyre::TuiHangouts::*)(); R = void; typename boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value), int>::type = int]'
/usr/include/boost/function/function_template.hpp:1071:16:   required from 'boost::function<R()>::function(Functor, typename boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value), int>::type) [with Functor = void (GekkoFyre::TuiHangouts::*)(); R = void; typename boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value), int>::type = int]'
/usr/include/boost/function/function_template.hpp:1126:5:   required from 'typename boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value), boost::function<R()>&>::type boost::function<R()>::operator=(Functor) [with Functor = void (GekkoFyre::TuiHangouts::*)(); R = void; typename boost::enable_if_c<(boost::type_traits::ice_not<(boost::is_integral<Functor>::value)>::value), boost::function<R()>&>::type = boost::function<void()>&]'
/usr/include/boost/signals2/detail/slot_template.hpp:160:24:   required from 'void boost::signals2::slot<R(Args ...), SlotFunction>::init_slot_function(const F&) [with F = void (GekkoFyre::TuiHangouts::*)(); SlotFunction = boost::function<void()>; R = void; Args = {}]'
/usr/include/boost/signals2/detail/slot_template.hpp:85:27:   required from 'boost::signals2::slot<R(Args ...), SlotFunction>::slot(const F&) [with F = void (GekkoFyre::TuiHangouts::*)(); SlotFunction = boost::function<void()>; R = void; Args = {}]'
/home/phobos/Programming/gecho/src/tui/chat.cpp:802:74:   required from here
/usr/include/boost/function/function_template.hpp:924:9: error: no class template named 'apply' in 'struct boost::detail::function::get_invoker0<boost::detail::function::member_ptr_tag>'
         handler_type;

如果有人能对此提供帮助，我们将不胜感激。正如我之前所说，我做了一些研究，但并没有真正找到任何东西。这对我来说似乎有点独特，也许，我确实严格按照教程进行操作。我知道这并不总是正确的做法，但根据我通过研究收集到的信息，这段代码应该可以工作。

Answer 1

&GekkoFyre::TuiHangouts::logMsgsDrawHistory 是一个成员函数指针，其类型为 void (GekkoFyre::TuiHangouts::*)()。这不像任何其他函数，因此不能像任何其他函数一样调用它。 Signals2 将尝试使用语法 func() 调用它，但这里没有 this 指针。要为其提供 this 指针，您可以使用语法 (p->*func)()。 p 在这里变成了 this 指针。 boost::bind(自 2011 年起在 C++ 标准中称为 std::bind)会将其包装为函数对象，可以通过调用 (p->*func)() 调用 func()。