operator ==容器迭代器const和非const

Question

我正在尝试为不可能的快速c ++委托提供一个事件管理器，本文中对此进行了讨论：http://blog.coldflake.com/posts/C++-delegates-on-steroids/ ；

template <typename T, typename R, typename... Params>
class delegate<R (T::*)(Params...) const>
{
public:
    typedef R (T::*func_type)(Params...) const;

    delegate(func_type func, const T& callee)
        : callee_(callee) , func_(func)
    {}

    R operator()(Params... args) const
    { return (callee_.*func_)(args...); }

    bool operator==(const delegate& other) const
    { return (&callee_ == &other.callee_) && (func_ == other.func_); }

    bool operator!= (const delegate& other) const
    { return !(*this == other); }

private:
    const T& callee_;
    func_type func_;
};

和我使用的方法之一；

using EventListenerDelegate = delegate<IEventDataPtr>;
using EventListenerList = std::list<EventListenerDelegate>;

bool EventManager::addListener(const EventListenerDelegate& eventDelegate, const EventType& type)
{
    // this will find or create the entry
    EventListenerList& eventListenerList = m_eventListeners[type];
    for (auto it = eventListenerList.begin(); it != eventListenerList.end(); ++it)
    {
        if (eventDelegate == (*it))
        {
            std::cout <<"Attempting to double-register a delegate" << std::endl;
            return false;
        }
    }
    eventListenerList.push_back(eventDelegate);
    return true;
}

代码无法编译，并显示gcc错误消息；

error: no match for 'operator==' (operand types are 'const EventListenerDelegate {aka const delegate<std::shared_ptr<IEventData> >}' and 'delegate<std::shared_ptr<IEventData> >')
         if (eventDelegate == (*it))
                           ^ 

我该怎么办才能解决该错误？ 谢谢。

编辑：代码中的其他两个专业模板；

//specialization for free functions
template <typename R, typename... Params>
class delegate<R (*)(Params...)>

和;

//specialization for member functions
template <typename T, typename R, typename... Params>
class delegate<R (T::*)(Params...)>