[Bug c++/71841] New: variadic template can't cast to base class

[johan.leroy at openehs dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71841

            Bug ID: 71841
           Summary: variadic template can't cast to base class
           Product: gcc
           Version: 5.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johan.leroy at openehs dot co.uk
  Target Milestone: ---

Also with version 6.0

Following example compiles and run on Visual Studio and CLang

template<IItem* ...aItem>
class Item : public IItem
{
private:
        static constexpr size_t c_NumberOfChilderen = (sizeof...(aItem) > 0 ?
sizeof...(aItem) : 1);
public:
        IItem* RootItem;
        IItem* ChildItem[c_NumberOfChilderen] = { aItem... };

        Item()
        {
                for (size_t x = 0; x < sizeof...(aItem); x++)
                {
                        ChildItem[x]->SetRoot(this);
                }
        }

        void printTree(int level)
        {
                for (int y = 0; y < level; y++)
                        printf("\t");
                printf("%p\n", this);
                for (size_t x = 0; x < sizeof...(aItem); x++)
                {
                        ChildItem[x]->printTree(level + 1);
                }
        }
        void SetRoot(IItem* RootItem)
        {
                RootItem = RootItem;
        }
private:

};




Item<> Level10;
Item<> Level11;
Item<reinterpret_cast<IItem*>(&Level11), reinterpret_cast<IItem*>(&Level10)>
ItemLevel00;

int main()
{
        ItemLevel00.printTree(0);
        return 0;
}


//Error from GCC

../src/main.cpp:53:76: error: could not convert template argument '(IItem*)(&
Level11)' to 'IItem*'
 Item<reinterpret_cast<IItem*>(&Level11), reinterpret_cast<IItem*>(&Level10)>
ItemLevel00;
                                                                            ^
../src/main.cpp:53:76: error: could not convert template argument '(IItem*)(&
Level10)' to 'IItem*'
../src/main.cpp: In function 'int main()':
../src/main.cpp:57:14: error: request for member 'printTree' in 'ItemLevel00',
which is of non-class type 'int'
  ItemLevel00.printTree(0);