...Pronounced any way you like, including "seventeen."
This library provides parsing and formatting for Roman numerals. According to my (probably extremely suspect) benchmarks, this is the best-performing library of its kind available on crates.io (you know, as of St. Patrick's Day, 2017 when I did the tests), so you should definitely employ it in your high-availability NAAS (numerals-as-a-service) project.
(Seriously, though, read the license--no warranties implied!)
Parsing is provided through Rust's ordinary FromStr trait, meaning you can create Roman values same as you create any other number--albeit with slightly simpler error cases, since the only possible errors are "Hey, that letter can't go in there," or "Dude, they go from 1 to 3999 and that's it!"
rust
let seventeen: Roman = "XVII".parse().unwrap();
There are several formatting options. Roman implements Display, which means that it'll work fine with println!("{}") et al., but for maximum efficiency (stop laughing!) I also provide two other functions: to_lowercase() and to_uppercase(). These skip the Display piping and just go straight into a new string.
Regarding formatting, there is one gotcha regarding the formatting of Roman values created via Roman::from_unchecked(): values that are less than the minimum printable value will come out as empty strings, while values that are larger will simply look like MMMMMMMMMMMMMMMXIV or something like that.
I'm thinking of stealing that feature from the other library where you can use the "{:x}" or "{:X}" formatters to choose upper vs. lower case in formatting.
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