C++ High Performance

Implementing a function using iterator categories

In order to read properties of an iterator, the STL class std::iterator_traits shall be utilized, not the raw iterator type. Correct: using Category = std::iterator_traits<Iterator>::iterator_categoryIncorrect: using Category = Iterator::iterator_category;

Let's say we want to implement a template function called iterator_distance(), equivalent of std::distance(), which returns the number of steps between two iterators:

• If the iterator category is random access we simply subtract the difference between the iterator a and b.
• Otherwise, we have to calculate the number of steps from iterator a to iterator b.

Using iterator_category tag and difference_type, the distance function is implemented ...