显式实例化声明是否需要“class”关键字？
template <class> class CL{};
template class CL<char>; //OK
template CL<int>; //without "class"; OK for VC and clang, wrong for gcc
显式实例化声明是否需要“class”关键字？
template <class> class CL{};
template class CL<char>; //OK
template CL<int>; //without "class"; OK for VC and clang, wrong for gcc