《Effective C++》Item 47

traits are always implemented as structs.

 

template<typename IterT>

void workWithIterator(IterT iter)
{
  typename std::iterator_traits<IterT>::value_type temp(*iter);
  ...
}

the C++ way of saying "the type of thing pointed to by objects of type IterT."

Template metaprogramming (TMP) is the process of writing template-based C++ programs that execute during compilation.