Ruby 3.2.0 Preview 3 Released

We are pleased to announce the release of Ruby 3.2.0-preview3. Ruby 3.2 adds many features and performance improvements.

WASI based WebAssembly support

This is an initial port of WASI based WebAssembly support. This enables a CRuby binary to be available on Web browser, Serverless Edge environment, and other WebAssembly/WASI embedders. Currently this port passes basic and bootstrap test suites not using Thread API.


WebAssembly (Wasm) is originally introduced to run programs safely and fast in web browsers. But its objective - running programs efficinently with security on various environment - is long wanted not only by web but also by general applications.

WASI (The WebAssembly System Interface) is designed for such use cases. Though such applications need to communicate with operating systems, WebAssembly runs on a virtual machine which didn’t have a system interface. WASI standardizes it.

WebAssembly/WASI Support in Ruby intends to leverage those projects. It enables Ruby developers to write applications which runs on such promised platform.

Use case

This support encourages developers can utilize CRuby in WebAssembly environment. An example use case of it is TryRuby playground’s CRuby support. Now you can try original CRuby in your web browser.

Technical points

Today’s WASI and WebAssembly itself has some missing features to implement Fiber, exception, and GC because it’s still evolving and also for security reasons. So CRuby fills the gap by using Asyncify, which is a binary transformation technique to control execution in userland.

In addition, we built a VFS on top of WASI so that we can easily pack Ruby apps into a single .wasm file. This makes distribution of Ruby apps a bit easier.

Related links

Regexp improvements against ReDoS

It is known that Regexp matching may take unexpectedly long. If your code attempts to match an possibly inefficient Regexp against an untrusted input, an attacker may exploit it for efficient Denial of Service (so-called Regular expression DoS, or ReDoS).

We have introduced two improvements that significantly mitigate ReDoS.

Improved Regexp matching algorithm

Since Ruby 3.2, Regexp’s matching algorithm has been greatly improved by using memoization technique.

# This matching takes 10 sec. in Ruby 3.1, and does 0.003 sec. in Ruby 3.2

/^a*b?a*$/ =~ "a" * 50000 + "x"

The improved matching algorithm allows most of Regexp matching (about 90% in our experiments) to be completed in linear time.

(For preview users: this optimization may consume memory proportional to the input length for each matching. We expect no practical problems to arise because this memory allocation is usually delayed, and a normal Regexp matching should consume at most 10 times as much memory as the input length. If you run out of memory when matching Regexps in a real-world application, please report it.)

The original proposal is

Regexp timeout

The optimization above cannot be applied to some kind of regular expressions, such as including advanced features (e.g., back-references or look-around), or with huge fixed number of repetitions. As a fallback measure, a timeout feature for Regexp matching is also introduced.

Regexp.timeout = 1.0

/^a*b?a*()\1$/ =~ "a" * 50000 + "x"
#=> Regexp::TimeoutError is raised in one second

Note that Regexp.timeout is a global configuration. If you want to use different timeout settings for some special Regexps, you may want to use timeout keyword for

Regexp.timeout = 1.0

# This regexp has no timeout
long_time_re ="^a*b?a*()\1$", timeout: Float::INFINITY)

long_time_re =~ "a" * 50000 + "x" # never interrupted

The original proposal is

Other Notable New Features

No longer bundle 3rd party sources

  • We no longer bundle 3rd party sources like libyaml, libffi.

    • libyaml source has been removed from psych. You may need to install libyaml-dev with Ubuntu/Debian platfrom. The package name is different each platforms.

    • bundled libffi source is also removed from fiddle


  • Anonymous rest and keyword rest arguments can now be passed as arguments, instead of just used in method parameters. [Feature #18351]

      def foo(*)
      def baz(**)
  • A proc that accepts a single positional argument and keywords will no longer autosplat. [Bug #18633]

    proc{|a, **k| a}.call([1, 2])
    # Ruby 3.1 and before
    # => 1
    # Ruby 3.2 and after
    # => [1, 2]
  • Constant assignment evaluation order for constants set on explicit objects has been made consistent with single attribute assignment evaluation order. With this code:

      foo::BAR = baz

    foo is now called before baz. Similarly, for multiple assignments to constants, left-to-right evaluation order is used. With this code:

        foo1::BAR1, foo2::BAR2 = baz1, baz2

    The following evaluation order is now used:

    1. foo1
    2. foo2
    3. baz1
    4. baz2

    [Bug #15928]

  • Find pattern is no longer experimental. [Feature #18585]

  • Methods taking a rest parameter (like *args) and wishing to delegate keyword arguments through foo(*args) must now be marked with ruby2_keywords (if not already the case). In other words, all methods wishing to delegate keyword arguments through *args must now be marked with ruby2_keywords, with no exception. This will make it easier to transition to other ways of delegation once a library can require Ruby 3+. Previously, the ruby2_keywords flag was kept if the receiving method took *args, but this was a bug and an inconsistency. A good technique to find the potentially-missing ruby2_keywords is to run the test suite, for where it fails find the last method which must receive keyword arguments, use puts nil, caller, nil there, and check each method/block on the call chain which must delegate keywords is correctly marked as ruby2_keywords. [Bug #18625] [Bug #16466]

      def target(**kw)
      # Accidentally worked without ruby2_keywords in Ruby 2.7-3.1, ruby2_keywords
      # needed in 3.2+. Just like (*args, **kwargs) or (...) would be needed on
      # both #foo and #bar when migrating away from ruby2_keywords.
      ruby2_keywords def bar(*args)
      ruby2_keywords def foo(*args)
      foo(k: 1)

Performance improvements


  • Support arm64 / aarch64 on UNIX platforms.
  • Building YJIT requires Rust 1.58.1+. [Feature #18481]

Other notable changes since 3.1

  • Hash
    • Hash#shift now always returns nil if the hash is empty, instead of returning the default value or calling the default proc. [Bug #16908]
  • MatchData
  • Module
  • Proc
  • Refinement
  • RubyVM::AbstractSyntaxTree
    • Add error_tolerant option for parse, parse_file and of. [Feature #19013]
  • Set
    • Set is now available as a builtin class without the need for require "set". [Feature #16989] It is currently autoloaded via the Set constant or a call to Enumerable#to_set.
  • String
    • String#byteindex and String#byterindex have been added. [Feature #13110]
    • Update Unicode to Version 14.0.0 and Emoji Version 14.0. [Feature #18037] (also applies to Regexp)
    • String#bytesplice has been added. [Feature #18598]
  • Struct
    • A Struct class can also be initialized with keyword arguments without keyword_init: true on [Feature #16806]

Compatibility issues

Note: Excluding feature bug fixes.

Removed constants

The following deprecated constants are removed.

Removed methods

The following deprecated methods are removed.

Stdlib compatibility issues

  • Psych no longer bundles libyaml sources. Users need to install the libyaml library themselves via the package system. [Feature #18571]

C API updates

Updated C APIs

The following APIs are updated.

  • PRNG update rb_random_interface_t updated and versioned. Extension libraries which use this interface and built for older versions. Also init_int32 function needs to be defined.

Removed C APIs

The following deprecated APIs are removed.

  • rb_cData variable.
  • “taintedness” and “trustedness” functions. [Feature #16131]

Standard libraries updates

  • SyntaxSuggest

    • The feature of syntax_suggest formerly dead_end is integrated in Ruby. [Feature #18159]
  • ErrorHighlight

    • Now it points an argument(s) of TypeError and ArgumentError
test.rb:2:in `+': nil can't be coerced into Integer (TypeError)

sum = ary[0] + ary[1]
  • The following default gems are updated.
    • RubyGems
    • bigdecimal 3.1.2
    • bundler
    • cgi 0.3.2
    • date 3.2.3
    • error_highlight 0.4.0
    • etc 1.4.0
    • io-console 0.5.11
    • io-nonblock 0.1.1
    • io-wait 0.3.0.pre
    • ipaddr 1.2.4
    • json 2.6.2
    • logger 1.5.1
    • net-http 0.2.2
    • net-protocol 0.1.3
    • ostruct 0.5.5
    • psych
    • reline 0.3.1
    • securerandom 0.2.0
    • set 1.0.3
    • stringio 3.0.3
    • syntax_suggest 0.0.1
    • timeout 0.3.0
  • The following bundled gems are updated.
    • minitest 5.16.3
    • net-imap 0.2.3
    • rbs 2.6.0
    • typeprof 0.21.3
    • debug 1.6.2
  • The following default gems are now bundled gems.

See NEWS or commit logs for more details.

With those changes, 2719 files changed, 191269 insertions(+), 120315 deletions(-) since Ruby 3.1.0!



    SIZE: 20086542
    SHA1: dafca8116d36ceaa32482ab38359768de8c3ae5e
    SHA256: c041d1488e62730d3a10dbe7cf7a3b3e4268dc867ec20ec991e7d16146640487
    SHA512: 860634d95e4b9c48f18d38146dfbdc3c389666d45454248a4ccdfc3a5d3cd0c71c73533aabf359558117de9add1472af228d8eaec989c9336b1a3a6f03f1ae88

    SIZE: 14799804
    SHA1: c94e2add05502cb5c39afffc995b7c8f000f7df0
    SHA256: d3f5619de544240d92a5d03aa289e71bd1103379622c523a0e80ed029a74b3bb
    SHA512: c1864e2e07c3711eaa17d0f85dfbcc6e0682b077782bb1c155315af45139ae66dc4567c73682d326975b0f472111eb0a70f949811cb54bed0b3a816ed6ac34df

    SIZE: 24426893
    SHA1: 346c051c4be7ab8d0b551fd2ff8169785697db62
    SHA256: cf49aa70e7ebd8abebffd5e49cd3bd92e5b9f3782d587cc7ed88c98dd5f17069
    SHA512: 4f22b5ea91be17ef5f68cf0acb1e3a226dcc549ad71cc9b40e623220087c4065ca9bea942710f668e5c94ca0323da8d2ccd565f95a9085c1a0e38e9c0543b22f

What is Ruby

Ruby was first developed by Matz (Yukihiro Matsumoto) in 1993, and is now developed as Open Source. It runs on multiple platforms and is used all over the world especially for web development.