Yep. And it's something of a known issue. Using BufReader#lines is glacial (and something of a known issue) in debug mode and merely slow in release mode. My understanding is that the BufReader is allocating a new String object for each line and so you're dealing with strict UTF-8 parsing and memory allocation.

My use case here is reading Vyatta config files. So lots of files that are generally (but not always) short. Mostly it's a fun teach myself Rust project, and it's hit lots of interesting edge cases in Rust, but otherwise I'd be all over just writing it in Python or Ruby.