SubscriptionManager.h

/* SubscriptionManager - Object that accepts subscriptions. */
 
#ifndef SubscriptionManager_H
#define SubscriptionManager_H
 
#include <set>
#include <cassert>
 
// Since this class has only POD types and no constructor, there's no
// initialize order problem.
template<class T>
class SubscriptionManager
{
  public:
    // TRICKY: If we make this a global instead of a global pointer,
    // then we'd have to be careful that the static constructors of all
    // subscribers are called before the collection constructor.  It's
    // impossible to enfore that in C++.  Instead, we'll allocate the
    // collection ourself on first use.  SubscriptionHandler itself is
    // a POD type, so a static SubscriptionHandler will always have
    // m_pSubscribers == NULL (before any static constructors are called).
    std::set<T*>* m_pSubscribers;
 
    // Use this to access m_pSubscribers, so you don't have to worry about
    // it being NULL.
    std::set<T*>& Get()
    {
        if (m_pSubscribers == nullptr)
            m_pSubscribers = new std::set<T*>;
        return *m_pSubscribers;
    }
 
    void Subscribe(T* p)
    {
        if (m_pSubscribers == nullptr)
            m_pSubscribers = new std::set<T*>;
#ifdef DEBUG
        typename set<T*>::iterator iter = m_pSubscribers->find(p);
        ASSERT_M(iter == m_pSubscribers->end(), "already subscribed");
#endif
        m_pSubscribers->insert(p);
    }
 
    void Unsubscribe(T* p)
    {
        auto iter = m_pSubscribers->find(p);
        assert(iter != m_pSubscribers->end());
        m_pSubscribers->erase(iter);
    }
};
 
#endif