使用带有限可变参数的模板函数限制允许的COM接口(std::is_same)

我有包装类,包含指向不同接口的COM指针(或智能指针)。

一些COM类可以从其他各种COM接口获得,我想用可变类型创建一个模板构造函数,它只允许传递适当类型的参数。

比如:

template <class T, class = typename 
   std::enable_if<std::is_base_of<IUnknown, T>::value>::type, class ... Types>
   class WithCOMptrbase
{
   protected:
   T* ptr_;

   public: 

   //construct smart pointer by copy
   WithCOMptrbase(T* ptr, bool AddRef = false)
     : ptr_(ptr)
   {
      if (AddRef) ptr_->AddRef();
   }

   /*construct a smart pointer by querying an interface from an argument of 
   a type which is the same as one of the variadics*/
   template <class TypeOther, class = typename
      std::enable_if<syd::is_same<Types... , TypeOther>::value... || 
      ...>::type> /*there needs to be a proper version*/
      WithCOMptrbase(TypeOther* ptr)
        : ptr_(cQueryInterface<T>(ptr))
      {}

//other methods
};

template <class U, class = typename 
   std::enable_if<std::is_base_of<IUnknown, U>::value>::type>
   T* cQueryInterface<T>(U *ptr)
{
   T* out;
   HRESULT hr = ptr->QueryInterface(__uuidof(T), (void**)&out);
   if (!SUCCEEED(hr)) throw _com_error(hr);
   return out;
}

因此,我将定义我的包装器类

class WrapperClass : protected WithCOMptrbase<IThis, IInterface1, IInterface2, IInterface3>
{
   //methods
};

到目前为止,我发现了以下线索: How to make a variadic is_same? 但它只是关于结构,而不是函数。

更新: 因为组合比继承更可取,所以我重新思考并决定使用模板函数而不是模板类。到目前为止,我已经成功地将给出的答案结合起来,并得出以下结论:

template <bool S, class Out, class Other, typename
std::enable_if<S>::type* = nullptr>
//copy-construct Smart Pointer for same Interfaces
WComPtr<Out> WFilterSame(const WComPtr<Other>& pOther)
{
    return WComPtr<Out>(pOther);
}

template <bool S, class Out, class Other, typename
    std::enable_if<!S>::type* = nullptr>
//Query Interface if differ
WComPtr<Out> WFilterSame(const WComPtr<Other>& pOther)
{
    return pOther.QueryInterface<Out>();
}

template <class Out, class ... Permitted, class Other>
WComPtr<Out> WFilterComInterfPtr(const WComPtr<Other>& pOther)
{

    static_assert(std::is_same<Out, Other>::value ||
        (std::is_same<Permitted, Other>::value || ...),
        "Interface is not supported.");

    return WFilterSame<std::is_same<Out, Other>::value, Out>(pOther);
}

class WComClass
{
   private:
   WComPtr<Interface> pComPtr_; //My Smart COM pointer

   template <class Other>
   WComPtr<Interface> WFilter(const WComPtr<Other>& pOther)
   {
      return WFilterComInterfPtr<Interface, IAllowed1, IAllowed2>(pOther);
   }

   public:
   template <class Other>
   WComClass(const WComPtr<Other>& pOther)
      : pComPtr_(WFilter(pOther))
   {}

   //methods
};

到目前为止,它的行为符合预期(wfiltercominerfptr),我不希望它在包装类构造函数中失败。