CppCon 2020

Writing standard-compliant iterators is surprisingly easy to get wrong. Standard containers are tedious to write, because they have such large interfaces, involving lots of similar operations. For many years, Boost.Iterator's iterator_facade and iterator_adaptor were the state of the art for automating the creation of iterators with minimal effort. However, that library has not kept up with the evolution of C++, particularly with regard to constexpr and noexcept.

Boost.STLInterfaces is a newly-accepted Boost library that solves these problems for authors of iterators and sequence containers. It does this using the same approach as C++20's std::ranges::view_interface. The view_interface template is a CRTP base that implements all the possible view member functions when inherited by a derived type containing just begin() and end(). This pattern allows the user to use Boost.STLInterfaces to write correct iterators, views, and/or sequence containers, requiring surprisingly little code.