This crate provides tools for compiling and using regular expressions. It is intended as a simple but compiler-checked version of the regex crate, as it does regular expression compilation at compile-time, but only supports POSIX Extended Regular Expressions.

Usage

use ere::prelude::*;

const PHONE_REGEX: Regex<2> = compile_regex!(r"^(\+1 )?[0-9]{3}-[0-9]{3}-[0-9]{4}$");
fn test() {
    assert!(PHONE_REGEX.test("012-345-6789"));
    assert!(PHONE_REGEX.test("987-654-3210"));
    assert!(PHONE_REGEX.test("+1 555-555-5555"));
    assert!(PHONE_REGEX.test("123-555-9876"));

    assert!(!PHONE_REGEX.test("abcd"));
    assert!(!PHONE_REGEX.test("0123456789"));
    assert!(!PHONE_REGEX.test("012--345-6789"));
    assert!(!PHONE_REGEX.test("(555) 555-5555"));
    assert!(!PHONE_REGEX.test("1 555-555-5555"));
}

const COLOR_REGEX: Regex<5> = compile_regex!(
    r"^#?([[:xdigit:]]{2})([[:xdigit:]]{2})([[:xdigit:]]{2})([[:xdigit:]]{2})?$"
);
fn exec() {
    assert_eq!(
        COLOR_REGEX.exec("#000000"),
        Some([
            Some("#000000"),
            Some("00"),
            Some("00"),
            Some("00"),
            None,
        ]),
    );
    assert_eq!(
        COLOR_REGEX.exec("1F2e3D"),
        Some([
            Some("1F2E3D"),
            Some("1F"),
            Some("2e"),
            Some("3D"),
            None,
        ]),
    );
    assert_eq!(
        COLOR_REGEX.exec("ffffff80"),
        Some([
            Some("ffffff80"),
            Some("ff"),
            Some("ff"),
            Some("ff"),
            Some("80"),
        ]),
    );

    assert_eq!(PHONE_REGEX.exec("green"), None);
    assert_eq!(PHONE_REGEX.exec("%FFFFFF"), None);
    assert_eq!(PHONE_REGEX.exec("#2"), None);
}

To minimize memory overhead and binary size, it is recommended to create a single instance of each regular expression (using a const variable) rather than creating multiple.

Roadmap

Features

• POSIX-compilant ambiguous submatching rules: we currently implement the Perl-like greedy submatching when submatches are ambiguous (this should only affect exec, not test, and only more complex regexes). While known implementations are more expensive, I plan on also supporting the POSIX rules.
• Case-insensitive mode: while regexes can be modified to support case-insensitivity (and this can also be done on ascii by just lower-casing the text first), I intend to implement case-insensitive mode.
• Non-capturing groups: (?:non-capturing) while not POSIX ERE standard-compilant, this is a relatively commonly used feature (and can improve performance by not tracking matches). If added, this will be behind a feature flag.

Performance Improvements

• u8-based engines: performance improvements can be made for many regexes (such as those with only ascii) by using u8s instead of extracting variably one to four-byte chars from strings.
• Additional limited-feature engines. This is relatively open-ended, but major improvements can be made for regexes with certain properties.

Alternatives

ere is intended as an alternative to regex that provides compile-time checking and regex compilation. However, ere is less featureful, so here are a few reasons you might prefer regex:

• You require more complex regular expressions with features like backreferences and word boundary checking (which are unavailable in POSIX EREs).
• You need run-time-compiled regular expressions (such as when provided by the user).
• Your regular expression runs significantly more efficiently on a specific regex engine not currently available in ere.