std.regex

Regular expressions in RE2's syntax, matched in linear time. Regex is a compiled pattern, Match one match with its groups, Matches the matches of a text in turn, and RegexError what a pattern that does not parse throws. A pattern is parsed into a tree, compiled into Thompson's NFA, and run by a Pike VM that carries the captures with each thread: every character of the text is looked at once per instruction at most, so (a*)*b over a hundred thousand a ends in milliseconds. There are no backreferences and no lookaround: they cannot be matched in linear time. Literals, ., classes ([a-z], [^…], \d \w \s and their capitals, [:alpha:] and the other POSIX names, \pL and \p{Lu} over the Unicode categories), groups (capturing, (?:…), (?P<name>…) and (?<name>…)), alternation, the repetitions * + ? {n} {n,} {n,m} each greedy or lazy with a ?, the anchors ^ $ \A \z, \b and \B, and the flags i m s inline ((?i), (?i:…), (?-i)). Positions are byte offsets into the text, as a string's indices are.

Examples

import std.io { println };
import std.regex { Regex, RegexError };

fn main(): void throws RegexError {
    let date = try Regex.new("(\\d{4})-(\\d{2})-(\\d{2})");
    let m = date.find("due 2026-10-24, paid") ?? panic("no date");
    println(m.group(1) ?? "");
    println(date.replaceAll("2026-10-24 and 2026-11-01", "${3}.${2}.${1}"));
}

2026
24.10.2026 and 01.11.2026

Types

RegexError struct — The error Regex.new throws: offset is where in the pattern, detail what is wrong there.

Match struct — A match: where it is in the text (byte offsets), its text, and its groups — group 0 the whole, a group that took no part null.

Regex class — A compiled regular expression.

Matches struct — The matches of a text in turn.