`std::iterator` Is Deprecated
In C++17 you must not derive from `std::iterator`. Instead it requires you to write the trait `typedefs` explicitly.
We'll cover the following...
The Standard Library API requires that each iterator type has to expose five typedefs:
iterator_category- the type of the iteratorvalue_type- type stored in the iteratordifference_type- the type that is the result of subtracting two iteratorspointer- pointer type of the stored typereference- the reference type of the stored type
iterator_category must be one of ...