#macro #lazy #static #regex


lazy static regular expressions checked at compile time

18 releases (stable)

2.4.1 Jan 5, 2023
2.3.1 Nov 4, 2022
2.3.0 Mar 5, 2022
2.2.2 Oct 20, 2021
0.1.2 Oct 7, 2019

#8 in Text processing

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Used in 122 crates (81 directly)

MIT license


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Use the regex! macro to build regexes:

  • they're checked at compile time
  • they're wrapped in once_cell lazy static initializers so that they're compiled only once
  • they can hold flags as suffix: let case_insensitive_regex = regex!("ab*"i);
  • regex creation is less verbose

This macro returns references to normal instances of regex::Regex so all the usual features are available.

You may also use shortcut macros for testing a match, replacing with concise closures, or capturing groups as substrings in some common situations:

  • regex_is_match!
  • regex_find!
  • regex_captures!
  • regex_replace!
  • regex_replace_all!

Some structs of the regex crate are reexported to ease dependency managment.

Build Regexes

use lazy_regex::regex;

// build a simple regex
let r = regex!("sa+$");
assert_eq!(r.is_match("Saa"), false);

// build a regex with flag(s)
let r = regex!("sa+$"i);
assert_eq!(r.is_match("Saa"), true);

// you can use a raw literal
let r = regex!(r#"^"+$"#);
assert_eq!(r.is_match("\"\""), true);

// or a raw literal with flag(s)
let r = regex!(r#"^\s*("[a-t]*"\s*)+$"#i);
assert_eq!(r.is_match(r#" "Aristote" "Platon" "#), true);

// there's no problem using the multiline definition syntax
let r = regex!(r#"(?x)
assert_eq!(r.find("This is lazy_regex-2.2!").unwrap().as_str(), "lazy_regex-2.2");
// (look at the regex_captures! macro to easily extract the groups)

// this line wouldn't compile because the regex is invalid:
// let r = regex!("(unclosed");

Supported regex flags: 'i', 'm', 's', 'x', 'U'.

See regex::RegexBuilder.

Test a match

use lazy_regex::regex_is_match;

let b = regex_is_match!("[ab]+", "car");
assert_eq!(b, true);

As for other macros, the main benefits here are that the regular expression is checked at compile time and compiled only once (lazily) in the life of your program.

Extract a value

use lazy_regex::regex_find;

let f_word = regex_find!(r#"\bf\w+\b"#, "The fox jumps.");
assert_eq!(f_word, Some("fox"));


use lazy_regex::regex_captures;

let (_, letter) = regex_captures!("([a-z])[0-9]+"i, "form A42").unwrap();
assert_eq!(letter, "A");

let (whole, name, version) = regex_captures!(
    r#"(\w+)-([0-9.]+)"#, // a literal regex
    "This is lazy_regex-2.0!", // any expression
assert_eq!(whole, "lazy_regex-2.0");
assert_eq!(name, "lazy_regex");
assert_eq!(version, "2.0");

There's no limit to the size of the tuple. It's checked at compile time to ensure you have the right number of capturing groups.

You receive "" for optional groups with no value.

Replace with captured groups

use lazy_regex::regex_replace_all;

let text = "Foo8 fuu3";
let text = regex_replace_all!(
    |_, name, digit| format!("F<{}>{}", name, digit),
assert_eq!(text, "F<oo>8 F<uu>3");

The number of arguments given to the closure is checked at compilation time to match the number of groups in the regular expression.

Shared lazy static

When a regular expression is used in several functions, you sometimes don't want to repeat it but have a shared static instance.

The regex! macro, while being backed by a lazy static regex, returns a reference.

If you want to have a shared lazy static regex, use the lazy_regex! macro:

use lazy_regex::*;

pub static GLOBAL_REX: Lazy<Regex> = lazy_regex!("^ab+$"i);

Like for the other macros, the regex is static, checked at compile time, and lazily built at first use.


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