模板函数在模板对象上执行成员回调而不提供它的实例

Question

一些上下文...

我有一个包含对象向量作为值的地图。
每个向量都包含特定类型的对象。
映射的键是代表每种类型的枚举值，EnumObjType
我正在接收包含 EnumObjType 和 ObjID 的事件。

我正在尝试构建一个模板函数来处理任何类型的对象，而我面临的挑战是这些对象 ID 是通过专用 class 的方法访问的。为了解决这个问题，我正在尝试向我的模板函数添加一个参数，该函数将被调用以获取 SpecializedObj 的 ID。

模板函数调用如下所示：

bool processEvent<SpecializedObj>(iEvent, iObjMap, &SpecializedObj::getSpecializedId);

定义：

template<typename ObjType>
bool processEvent(MyEvent* iEvent,  ObjMap* iObjMap, std::function<unsigned int(void)> iObjIdCall)
{
  // Reach the corresponding ObjType vector
  ObjMap::iterator it =  iObjMap->find(iEvent->getObjType());
  std::vector<BaseObject*> wObjVector = it->second;

  // Iterate over the vector's range  
  for(BaseObject* wBaseObjPtr : wObjVector)
  {
    // Cast into SpecializedObj
    ObjType* wSpecializedObjPtr = dynamic_cast<ObjType*>(wBaseObjPtr);

    // Test dynamic_cast result
    if(!wSpecializedObjPtr) {return false;}

    std::function<unsigned int(void)> callback = std::bind(iObjIdCall,*wSpecializedObjPtr);

    // Check if the SpecializedObjPtr's ID matches the event's DeviceId
    if(callback() != iEvent->getDeviceId()) {return false;}

    // work on SpecializedObj
    // ...
    return true
  }

下面是我眼中相当神秘的错误：

11>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(514) : error C2664: 'std::_Func_class<_Ret>::_Set' : cannot convert parameter 1 from '_Myimpl *' to 'std::_Func_base<_Rx> *'
11>        with
11>        [
11>            _Ret=const unsigned int
11>        ]
11>        and
11>        [
11>            _Rx=const unsigned int
11>        ]
11>        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
11>        C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(514) : see reference to function template instantiation 'void std::_Func_class<_Ret>::_Do_alloc<_Myimpl,_Fret(__thiscall SpecializedObj::* const &)(void) const,_Alloc>(_Fty,_Alloc)' being compiled
11>        with
11>        [
11>            _Ret=const unsigned int,
11>            _Fret=const unsigned int,
11>            _Alloc=std::allocator<std::_Func_class<const unsigned int>>,
11>            _Fty=const unsigned int (__thiscall SpecializedObj::* const &)(void) const
11>        ]
11>        C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(514) : see reference to function template instantiation 'void std::_Func_class<_Ret>::_Do_alloc<_Myimpl,_Fret(__thiscall SpecializedObj::* const &)(void) const,_Alloc>(_Fty,_Alloc)' being compiled
11>        with
11>        [
11>            _Ret=const unsigned int,
11>            _Fret=const unsigned int,
11>            _Alloc=std::allocator<std::_Func_class<const unsigned int>>,
11>            _Fty=const unsigned int (__thiscall SpecializedObj::* const &)(void) const
11>        ]
11>        C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(514) : see reference to function template instantiation 'void std::_Func_class<_Ret>::_Reset_alloc<_Fret,SpecializedObj,std::allocator<_Ty>>(_Fret (__thiscall SpecializedObj::* const )(void) const,_Alloc)' being compiled
11>        with
11>        [
11>            _Ret=const unsigned int,
11>            _Fret=const unsigned int,
11>            _Ty=std::_Func_class<const unsigned int>,
11>            _Alloc=std::allocator<std::_Func_class<const unsigned int>>
11>        ]
11>        C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(514) : see reference to function template instantiation 'void std::_Func_class<_Ret>::_Reset_alloc<_Fret,SpecializedObj,std::allocator<_Ty>>(_Fret (__thiscall SpecializedObj::* const )(void) const,_Alloc)' being compiled
11>        with
11>        [
11>            _Ret=const unsigned int,
11>            _Fret=const unsigned int,
11>            _Ty=std::_Func_class<const unsigned int>,
11>            _Alloc=std::allocator<std::_Func_class<const unsigned int>>
11>        ]
11>        C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(675) : see reference to function template instantiation 'void std::_Func_class<_Ret>::_Reset<const unsigned int,SpecializedObj>(_Fret (__thiscall SpecializedObj::* const )(void) const)' being compiled
11>        with
11>        [
11>            _Ret=const unsigned int,
11>            _Fret=const unsigned int
11>        ]
11>        C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\functional(675) : see reference to function template instantiation 'void std::_Func_class<_Ret>::_Reset<const unsigned int,SpecializedObj>(_Fret (__thiscall SpecializedObj::* const )(void) const)' being compiled
11>        with
11>        [
11>            _Ret=const unsigned int,
11>            _Fret=const unsigned int
11>        ]
11>        C:\MyProject\ObjUpdater.cpp(29) : see reference to function template instantiation 'std::function<_Fty>::function<const unsigned int(__thiscall SpecializedObj::* )(void) const>(_Fx &&)' being compiled
11>        with
11>        [
11>            _Fty=const unsigned int (void),
11>            _Fx=const unsigned int (__thiscall SpecializedObj::* )(void) const
11>        ]
11>        C:\MyProject\ObjUpdater.cpp(29) : see reference to function template instantiation 'std::function<_Fty>::function<const unsigned int(__thiscall SpecializedObj::* )(void) const>(_Fx &&)' being compiled
11>        with
11>        [
11>            _Fty=const unsigned int (void),
11>            _Fx=const unsigned int (__thiscall SpecializedObj::* )(void) const
11>        ]

当我以前使用回调时，我总是知道它会与哪个对象实例相关联，所以我将它作为函数参数传递给 std::bind(&Foo::func, fooObj)，但它在这里似乎对我不起作用.

编辑：我正在使用 Visual Studio 2012 v110 工具集

Answer 1

When I had previously worked with callbacks, I always knew with what object instance it would be associated, so I'd pass it as function parameters with std::bind(&Foo::func, fooObj) but it does not seem to work for me here.

如果 processEvent() 将 iObjIdCall 作为 std::function<unsigned int(void)> 接收，当您尝试绑定它并保存 std::bind() 结果为相同类型的对象时

std::function<unsigned int(void)> callback
    = std::bind(iObjIdCall,*wSpecializedObjPtr);

你混淆了编译器。

尝试将 processEvent() 定义为接收指向方法的指针而不是 std::function；像

template <typename ObjType>
bool processEvent (MyEvent* iEvent,  ObjMap* iObjMap, ObjType::*iObjIdCall)

如果我没有记错的话。

模板函数在模板对象上执行成员回调而不提供它的实例

Template function to execute member callback on templated object without providing it's instance

c++

templates

callback

stdbind

c++11