Over the last several years, I’ve rewritten Rust’s regex crate to enable better internal composition, and to make it easier to add optimizations while maintaining correctness. In the course of this rewrite I created a new crate, regex-automata, which exposes much of the regex crate internals as their own APIs for others to use. To my knowledge, this is the first regex library to expose its internals to the degree done in regex-automata as a separately versioned library.

This blog post discusses the problems that led to the rewrite, how the rewrite solved them and a guided tour of regex-automata’s API.

Target audience: Rust programmers and anyone with an interest in how one particular finite automata regex engine is implemented. Prior experience with regular expressions is assumed.