CODEWITHSUNDEEP
c++macros
Dekakaruk
Dekakaruk

Reputation: 717

C++ macro defining classes dependent on each other

I'm trying to write macro that defines two tightly connected classes at once, but I cannot. Here is my code:

#ifndef SIGNALS_HPP
#define SIGNALS_HPP

#include <unordered_set>
#include <cstdio>

/**
  * Macro defines pair of classes, sender and receiver. When one of them is destroyed, 
  * all it's connections are dully unconnected.
  * 
  * EXAMPLE:
  * 
  *     signal(SomeEvent, some_event_occured)
  * 
  * EXPANDS TO:
  *     
  *     class SomeEventReceiver {
  *     protected:
  *         virtual void on_some_event_occured() {}
  *     }
  * 
  *     class SomeEventSender {
  *     public:
  *         void connect_some_event_occured(SomeEventReceiver & listener);  // registers listener
  *         void unconnect_some_event_occured(SomeEventReceiver & listener);  // forgets listener
  *     
  *     protected:
  *         void send_some_event_occured();  // notifies all listeners
  *     }
  */

#define signal(signal_name, slot_name)\
    class signal_name##Sender;\
    \
    class signal_name##Receiver\
    {\
        friend class signal_name##Sender;\
        std::unordered_set<signal_name##Sender*> senders;\
        \
    protected:\
        virtual void on_##slot_name() {}\
        \
    public:\
        virtual ~signal_name##Receiver();\
    };\
    \
    \
    class signal_name##Sender\
    {\
        friend class signal_name##Receiver;\
        std::unordered_set<signal_name##Receiver*> listeners;\
        \
    public:\
        virtual ~signal_name##Sender()\
        {\
            for (auto i : listeners)\
                i->senders.erase(this);\
            listeners.clear();\
        }\
        \
        void connect_##slot_name(signal_name##Receiver & listener)\
        {\
            listeners.insert(&listener);\
            listener.senders.insert(this);\
        }\
    \
        void unconnect_##slot_name(signal_name##Receiver & listener)\
        {\
            listeners.erase(&listener);\
            listener.senders.erase(this);\
        }\
        \
    protected: \
        void send_##slot_name()\
        {\
            for (auto i : listeners)\
                i->on_##slot_name();\
        }\
        \
    };\
    \
    /*\ //  <--------------  THE LAST SECTION
    signal_name##Receiver::~signal_name##Receiver()\
    {\
        for (auto i : senders)\
            i->listeners.erase(this);\
        senders.clear();\
    }//*/\




#endif // SIGNALS_HPP

1) Why it does work with the last section commented? I thought that all virtual methods must be either defined or pure?

2) This macro is used in another header. When the last section is uncommented I receive a lot of "multiple definition" errors. I belive I know why it does not work: the last section counts as definition and should not be in header. But then how can I implement such macro? Or if I'm mistaken, what is the real problem?

Quick usage example:

#ifndef SOME_HPP
#define SOME_HPP

signal(AA, aa)

class X : public AASender {
};

#endif

If something like that is included (maybe indirectly) in a few .cpp files it gets errors of kind: "multiple definition of typeinfo for AAReceiver', first defined here, In function~new_allocator':". "typeinfo" varies to destructor andtype name and vtable. AAReciver sometimes becomes AASender.

If someone really likes reading there are real errors:

army.o: In function `~BattleEndaaaaaaaReceiver':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
army.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
army.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
army.o: In function `std::__detail::_Hashtable_alloc<std::allocator<std::__detail::_Hash_node<BattleEndaaaaaaaSender*, false> > >::_M_deallocate_nodes(std::__detail::_Hash_node<BattleEndaaaaaaaSender*, false>*)':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
army.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo name for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
army.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `vtable for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
game.o: In function `~BattleEndaaaaaaaReceiver':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
game.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
game.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
game.o: In function `vector':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
game.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo name for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
game.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `vtable for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
gamemapwidget.o: In function `~BattleEndaaaaaaaReceiver':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
gamemapwidget.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
gamemapwidget.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
gamemapwidget.o: In function `std::_Hashtable<BattleEndaaaaaaaReceiver*, BattleEndaaaaaaaReceiver*, std::allocator<BattleEndaaaaaaaReceiver*>, std::__detail::_Identity, std::equal_to<BattleEndaaaaaaaReceiver*>, std::hash<BattleEndaaaaaaaReceiver*>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::_M_erase(std::integral_constant<bool, true>, BattleEndaaaaaaaReceiver* const&)':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
gamemapwidget.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo name for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
gamemapwidget.o: In function `new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `vtable for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
battle.o: In function `~BattleEndaaaaaaaReceiver':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
battle.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
battle.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `BattleEndaaaaaaaReceiver::~BattleEndaaaaaaaReceiver()'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
battle.o: In function `std::__detail::_Hashtable_alloc<std::allocator<std::__detail::_Hash_node<BattleEndaaaaaaaSender*, false> > >::_M_deallocate_nodes(std::__detail::_Hash_node<BattleEndaaaaaaaSender*, false>*)':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
battle.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `typeinfo name for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
battle.o: In function `~new_allocator':
/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: multiple definition of `vtable for BattleEndaaaaaaaReceiver'
province.o:/home/michal/Dokumenty/Projekty/build-Universania-Desktop-Debug/../Universania/battle.hpp:10: first defined here
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Upvotes: 1

Views: 619

Answers (1)

Walter
Walter

Reputation: 45414

An out-of-line function definition in a header will be emited with every compilation unit that includes that header, hence the multiple definitions. Simply make it inline to avoid that.

Btw, this has nothing to do with your macro. Macros should be avoided in C++. Except for include guards and conditional compilation, there are almost no sensible macro usages in C++. Many things can be better done with templates.

Upvotes: 3

Related Questions