1.1.0 (2018-11-30)

This is a small release with a couple small enhancements. This release also increases the minimal supported Rust version (MSRV) to 1.24.1 (from 1.20.0). In accordance with this crate's MSRV policy, this release bumps the minor version number.

Performance improvements:

New features:

Bug fixes:

  • BUG #530: Add Unicode license (for data tables).
  • Various typo/doc fixups.

1.0.6 (2018-11-06)

This is a small release.

Performance improvements:

  • OPT #513: Improve performance of compiling large Unicode classes by 8-10%.

Bug fixes:

  • BUG #533: Fix definition of [[:blank:]] class that regressed in regex-syntax 0.5.

1.0.5 (2018-09-06)

This is a small release with an API enhancement.

New features:

1.0.4 (2018-08-25)

This is a small release that bumps the quickcheck dependency.

1.0.3 (2018-08-24)

This is a small bug fix release.

Bug fixes:

  • BUG #504: Fix for Cargo's “minimal version” support.
  • BUG 1e39165f: Fix doc examples for byte regexes.

1.0.2 (2018-07-18)

This release exposes some new lower level APIs on Regex that permit amortizing allocation and controlling the location at which a search is performed in a more granular way. Most users of the regex crate will not need or want to use these APIs.

New features:

  • FEATURE #493: Add a few lower level APIs for amortizing allocation and more fine grained searching.

Bug fixes:

  • BUG 3981d2ad: Correct outdated documentation on RegexBuilder::dot_matches_new_line.
  • BUG 7ebe4ae0: Correct outdated documentation on Parser::allow_invalid_utf8 in the regex-syntax crate.
  • BUG 24c7770b: Fix a bug in the HIR printer where it wouldn't correctly escape meta characters in character classes.

1.0.1 (2018-06-19)

This release upgrades regex's Unicode tables to Unicode 11, and enables SIMD optimizations automatically on Rust stable (1.27 or newer).

New features:

  • FEATURE #486: Implement size_hint on RegexSet match iterators.
  • FEATURE #488: Update Unicode tables for Unicode 11.
  • FEATURE #490: SIMD optimizations are now enabled automatically in Rust stable, for versions 1.27 and up. No compilation flags or features need to be set. CPU support SIMD is detected automatically at runtime.

Bug fixes:

  • BUG #482: Present a better compilation error when the use_std feature isn't used.

1.0.0 (2018-05-01)

This release marks the 1.0 release of regex.

While this release includes some breaking changes, most users of older versions of the regex library should be able to migrate to 1.0 by simply bumping the version number. The important changes are as follows:

  • We adopt Rust 1.20 as the new minimum supported version of Rust for regex. We also tentativley adopt a policy that permits bumping the minimum supported version of Rust in minor version releases of regex, but no patch releases. That is, with respect to semver, we do not strictly consider bumping the minimum version of Rust to be a breaking change, but adopt a conservative stance as a compromise.
  • Octal syntax in regular expressions has been disabled by default. This permits better error messages that inform users that backreferences aren't available. Octal syntax can be re-enabled via the corresponding option on RegexBuilder.
  • (?-u:\B) is no longer allowed in Unicode regexes since it can match at invalid UTF-8 code unit boundaries. (?-u:\b) is still allowed in Unicode regexes.
  • The From<regex_syntax::Error> impl has been removed. This formally removes the public dependency on regex-syntax.
  • A new feature, use_std, has been added and enabled by default. Disabling the feature will result in a compilation error. In the future, this may permit us to support no_std environments (w/ alloc) in a backwards compatible way.

For more information and discussion, please see 1.0 release tracking issue.

0.2.11 (2018-05-01)

This release primarily contains bug fixes. Some of them resolve bugs where the parser could panic.

New features:

  • FEATURE #459: Include C++‘s standard regex library and Boost’s regex library in the benchmark harness. We now include D/libphobos, C++/std, C++/boost, Oniguruma, PCRE1, PCRE2, RE2 and Tcl in the harness.

Bug fixes:

  • BUG #445: Clarify order of indices returned by RegexSet match iterator.
  • BUG #461: Improve error messages for invalid regexes like [\d-a].
  • BUG #464: Fix a bug in the error message pretty printer that could cause a panic when a regex contained a literal \n character.
  • BUG #465: Fix a panic in the parser that was caused by applying a repetition operator to (?flags).
  • BUG #466: Fix a bug where \pC was not recognized as an alias for \p{Other}.
  • BUG #470: Fix a bug where literal searches did more work than necessary for anchored regexes.

0.2.10 (2018-03-16)

This release primarily updates the regex crate to changes made in std::arch on nightly Rust.

New features:

  • FEATURE #458: The Hir type in regex-syntax now has a printer.

0.2.9 (2018-03-12)

This release introduces a new nightly only feature, unstable, which enables SIMD optimizations for certain types of regexes. No additional compile time options are necessary, and the regex crate will automatically choose the best CPU features at run time. As a result, the simd (nightly only) crate dependency has been dropped.

New features:

  • FEATURE #456: The regex crate now includes AVX2 optimizations in addition to the extant SSSE3 optimization.

Bug fixes:

  • BUG #455: Fix a bug where (?x)[ / - ] failed to parse.

0.2.8 (2018-03-12)

Bug gixes:

  • BUG #454: Fix a bug in the nest limit checker being too aggressive.

0.2.7 (2018-03-07)

This release includes a ground-up rewrite of the regex-syntax crate, which has been in development for over a year.

New features:

  • Error messages for invalid regexes have been greatly improved. You get these automatically; you don't need to do anything. In addition to better formatting, error messages will now explicitly call out the use of look around. When regex 1.0 is released, this will happen for backreferences as well.
  • Full support for intersection, difference and symmetric difference of character classes. These can be used via the &&, -- and ~~ binary operators within classes.
  • A Unicode Level 1 conformat implementation of \p{..} character classes. Things like \p{scx:Hira}, \p{age:3.2} or \p{Changes_When_Casefolded} now work. All property name and value aliases are supported, and properties are selected via loose matching. e.g., \p{Greek} is the same as \p{G r E e K}.
  • A new UNICODE.md document has been added to this repository that exhaustively documents support for UTS#18.
  • Empty sub-expressions are now permitted in most places. That is, ()+ is now a valid regex.
  • Almost everything in regex-syntax now uses constant stack space, even when performing anaylsis that requires structural induction. This reduces the risk of a user provided regular expression causing a stack overflow.
  • FEATURE #174: The Ast type in regex-syntax now contains span information.
  • FEATURE #424: Support \u, \u{...}, \U and \U{...} syntax for specifying code points in a regular expression.
  • FEATURE #449: Add a Replace::by_ref adapter for use of a replacer without consuming it.

Bug fixes:

  • BUG #446: We re-enable the Boyer-Moore literal matcher.

0.2.6 (2018-02-08)

Bug fixes:

  • BUG #446: Fixes a bug in the new Boyer-Moore searcher that results in a match failure. We fix this bug by temporarily disabling Boyer-Moore.

0.2.5 (2017-12-30)

Bug fixes:

  • BUG #437: Fixes a bug in the new Boyer-Moore searcher that results in a panic.

0.2.4 (2017-12-30)

New features:

  • FEATURE #348: Improve performance for capture searches on anchored regex. (Contributed by @ethanpailes. Nice work!)
  • FEATURE #419: Expand literal searching to include Tuned Boyer-Moore in some cases. (Contributed by @ethanpailes. Nice work!)

Bug fixes:

  • BUG: The regex compiler plugin has been removed.
  • BUG: simd has been bumped to 0.2.1, which fixes a Rust nightly build error.
  • BUG: Bring the benchmark harness up to date.

0.2.3 (2017-11-30)

New features:

Bug fixes:

  • BUG #375: Fix a bug that prevented the bounded backtracker from terminating.
  • BUG #393, BUG #394: Fix bug with replace methods for empty matches.

0.2.2 (2017-05-21)

New features:

  • FEATURE #341: Support nested character classes and intersection operation. For example, [\p{Greek}&&\pL] matches greek letters and [[0-9]&&[^4]] matches every decimal digit except 4. (Much thanks to @robinst, who contributed this awesome feature.)

Bug fixes:

  • BUG #321: Fix bug in literal extraction and UTF-8 decoding.
  • BUG #326: Add documentation tip about the (?x) flag.
  • BUG #333: Show additional replacement example using curly braces.
  • BUG #334: Fix bug when resolving captures after a match.
  • BUG #338: Add example that uses Captures::get to API documentation.
  • BUG #353: Fix RegexSet bug that caused match failure in some cases.
  • BUG #354: Fix panic in parser when (?x) is used.
  • BUG #358: Fix literal optimization bug with RegexSet.
  • BUG #359: Fix example code in README.
  • BUG #365: Fix bug in rure_captures_len in the C binding.
  • BUG #367: Fix byte class bug that caused a panic.


One major bug with replace_all has been fixed along with a couple of other touchups.

  • BUG #312: Fix documentation for NoExpand to reference correct lifetime parameter.
  • BUG #314: Fix a bug with replace_all when replacing a match with the empty string.
  • BUG #316: Note a missing breaking change from the 0.2.0 CHANGELOG entry. (RegexBuilder::compile was renamed to RegexBuilder::build.)
  • BUG #324: Compiling regex should only require one version of memchr crate.


This is a new major release of the regex crate, and is an implementation of the regex 1.0 RFC. We are releasing a 0.2 first, and if there are no major problems, we will release a 1.0 shortly. For 0.2, the minimum supported Rust version is 1.12.

There are a number of breaking changes in 0.2. They are split into two types. The first type correspond to breaking changes in regular expression syntax. The second type correspond to breaking changes in the API.

Breaking changes for regex syntax:

  • POSIX character classes now require double bracketing. Previously, the regex [:upper:] would parse as the upper POSIX character class. Now it parses as the character class containing the characters :upper:. The fix to this change is to use [[:upper:]] instead. Note that variants like [[:upper:][:blank:]] continue to work.
  • The character [ must always be escaped inside a character class.
  • The characters &, - and ~ must be escaped if any one of them are repeated consecutively. For example, [&], [\&], [\&\&], [&-&] are all equivalent while [&&] is illegal. (The motivation for this and the prior change is to provide a backwards compatible path for adding character class set notation.)
  • A bytes::Regex now has Unicode mode enabled by default (like the main Regex type). This means regexes compiled with bytes::Regex::new that don't have the Unicode flag set should add (?-u) to recover the original behavior.

Breaking changes for the regex API:

  • find and find_iter now return Match values instead of (usize, usize). Match values have start and end methods, which return the match offsets. Match values also have an as_str method, which returns the text of the match itself.
  • The Captures type now only provides a single iterator over all capturing matches, which should replace uses of iter and iter_pos. Uses of iter_named should use the capture_names method on Regex.
  • The at method on the Captures type has been renamed to get, and it now returns a Match. Similarly, the name method on Captures now returns a Match.
  • The replace methods now return Cow values. The Cow::Borrowed variant is returned when no replacements are made.
  • The Replacer trait has been completely overhauled. This should only impact clients that implement this trait explicitly. Standard uses of the replace methods should continue to work unchanged. If you implement the Replacer trait, please consult the new documentation.
  • The quote free function has been renamed to escape.
  • The Regex::with_size_limit method has been removed. It is replaced by RegexBuilder::size_limit.
  • The RegexBuilder type has switched from owned self method receivers to &mut self method receivers. Most uses will continue to work unchanged, but some code may require naming an intermediate variable to hold the builder.
  • The compile method on RegexBuilder has been renamed to build.
  • The free is_match function has been removed. It is replaced by compiling a Regex and calling its is_match method.
  • The PartialEq and Eq impls on Regex have been dropped. If you relied on these impls, the fix is to define a wrapper type around Regex, impl Deref on it and provide the necessary impls.
  • The is_empty method on Captures has been removed. This always returns false, so its use is superfluous.
  • The Syntax variant of the Error type now contains a string instead of a regex_syntax::Error. If you were examining syntax errors more closely, you'll need to explicitly use the regex_syntax crate to re-parse the regex.
  • The InvalidSet variant of the Error type has been removed since it is no longer used.
  • Most of the iterator types have been renamed to match conventions. If you were using these iterator types explicitly, please consult the documentation for its new name. For example, RegexSplits has been renamed to Split.

A number of bugs have been fixed:

  • BUG #151: The Replacer trait has been changed to permit the caller to control allocation.
  • BUG #165: Remove the free is_match function.
  • BUG #166: Expose more knobs (available in 0.1) and remove with_size_limit.
  • BUG #168: Iterators produced by Captures now have the correct lifetime parameters.
  • BUG #175: Fix a corner case in the parsing of POSIX character classes.
  • BUG #178: Drop the PartialEq and Eq impls on Regex.
  • BUG #179: Remove is_empty from Captures since it always returns false.
  • BUG #276: Position of named capture can now be retrieved from a Captures.
  • BUG #296: Remove winapi/kernel32-sys dependency on UNIX.
  • BUG #307: Fix error on emscripten.


  • PR #292: Fixes bug #291, which was introduced by PR #290.


  • Require regex-syntax 0.3.8.


  • PR #290: Fixes bug #289, which caused some regexes with a certain combination of literals to match incorrectly.


  • PR #281: Fixes bug #280 by disabling all literal optimizations when a pattern is partially anchored.


  • Tweak criteria for using the Teddy literal matcher.


  • PR #275: Improves match verification performance in the Teddy SIMD searcher.
  • PR #278: Replaces slow substring loop in the Teddy SIMD searcher with Aho-Corasick.
  • Implemented DoubleEndedIterator on regex set match iterators.


  • Release regex-syntax 0.3.5 with a minor bug fix.
  • Fix bug #272.
  • Fix bug #277.
  • PR #270: Fixes bugs #264, #268 and an unreported where the DFA cache size could be drastically under estimated in some cases (leading to high unexpected memory usage).


  • Release regex-syntax 0.3.4.
  • Bump regex-syntax dependency version for regex to 0.3.4.


  • PR #262: Fixes a number of small bugs caught by fuzz testing (AFL).


  • PR #236: Fix a bug in how suffix literals were extracted, which could lead to invalid match behavior in some cases.


  • PR #231: Add SIMD accelerated multiple pattern search.
  • PR #228: Reintroduce the reverse suffix literal optimization.
  • PR #226: Implements NFA state compression in the lazy DFA.
  • PR #223: A fully anchored RegexSet can now short-circuit.


  • PR #216: Tweak the threshold for running backtracking.
  • PR #217: Add upper limit (from the DFA) to capture search (for the NFA).
  • PR #218: Add rure, a C API.


  • PR #210: Fixed a performance bug in bytes::Regex::replace where extend was used instead of extend_from_slice.
  • PR #211: Fixed a bug in the handling of word boundaries in the DFA.
  • PR #213: Added RE2 and Tcl to the benchmark harness. Also added a CLI utility from running regexes using any of the following regex engines: PCRE1, PCRE2, Oniguruma, RE2, Tcl and of course Rust's own regexes.


  • PR #201: Fix undefined behavior in the regex! compiler plugin macro.
  • PR #205: More improvements to DFA performance. Competitive with RE2. See PR for benchmarks.
  • PR #209: Release 0.1.66 was semver incompatible since it required a newer version of Rust than previous releases. This PR fixes that. (And 0.1.66 was yanked.)


  • Speculative support for Unicode word boundaries was added to the DFA. This should remove the last common case that disqualified use of the DFA.
  • An optimization that scanned for suffix literals and then matched the regular expression in reverse was removed because it had worst case quadratic time complexity. It was replaced with a more limited optimization where, given any regex of the form re$, it will be matched in reverse from the end of the haystack.
  • PR #202: The inner loop of the DFA was heavily optimized to improve cache locality and reduce the overall number of instructions run on each iteration. This represents the first use of unsafe in regex (to elide bounds checks).
  • PR #200: Use of the mempool crate (which used thread local storage) was replaced with a faster version of a similar API in @Amanieu's thread_local crate. It should reduce contention when using a regex from multiple threads simultaneously.
  • PCRE2 JIT benchmarks were added. A benchmark comparison can be found here. (Includes a comparison with PCRE1's JIT and Oniguruma.)
  • A bug where word boundaries weren't being matched correctly in the DFA was fixed. This only affected use of bytes::Regex.
  • #160: Captures now has a Debug impl.