Lua string patterns in Rust

Lua string patterns are a powerful yet lightweight alternative to full regular expressions. They are not regexps, since there is no alternation (the | operator), but this is not usually a problem. In fact, full regexps become too powerful and power can be dangerous or just plain confusing. This is why OpenBSD's httpd has Lua patterns. The decision to use % as the escape rather than the traditional \ is refreshing. In the Rust context, lua-patterns is a very lightweight dependency, if you don't need the full power of the regex crate.

This library reuses the original source from Lua 5.2 - only 400 lines of battle-tested C. I originally did this for a similar project to bring these patterns to C++.

More information can be found on the Lua wiki.

I've organized the Rust interface much as the original Lua library, 'match', 'gmatch' and 'gsub', but made these methods of a LuaPattern struct. This is for two main reasons:

• although string patterns are not compiled, they can be validated upfront
• after a match, the struct contains the results

extern crate lua_patterns;
use lua_patterns::LuaPattern;

let mut m = LuaPattern::new("one");
let text = "hello one two";
assert!(m.matches(text));
let r = m.range();
assert_eq!(r.start, 6);
assert_eq!(r.end, 9);

This not in itself impressive, since it can be done with the string find method, but once we start using patterns it gets more exciting, especially with captures:

let mut m = LuaPattern::new("(%a+) one");
let text = " hello one two";
assert!(m.matches(text));
assert_eq!(m.capture(0),1..10); // "hello one"
assert_eq!(m.capture(1),1..6); // "hello"

Lua patterns (like regexps) are not anchored by default, so this finds the first match and works from there. The 0 capture always exists (the full match) and here the 1 capture just picks up the first word.