16.1.5 控制实例化

template <typename T>class Blob {public:    T sum(T a, T b);};template <typename T> T Blob<T>::sum(T a, T b){    return a + b;}template <>class Blob<int> {public:    int sum(int a, int b);};int Blob<int>::sum(int a, int b){    return a + b;}//extern template class Blob<int>;