You might be wondering: "Every iterator class I implement needs to provide the same five member typedefs. That's a lot of boilerplate--a lot of typing that I'd like to factor out, if I could." Is there no way to eliminate all that boilerplate?
Well, in C++98, and up until C++17, the standard library included a helper class template to do exactly that. Its name was std::iterator, and it took five template type parameters that corresponded to the five member typedefs required by std::iterator_traits. Three of these parameters had "sensible defaults," meaning that the simplest use-case was pretty well covered:
namespace std { template< class Category, class T, class Distance = std::ptrdiff_t, class Pointer = T*, ...
