Ruby 3.1.0 Preview 1 Released

We are pleased to announce the release of Ruby 3.1.0-preview1.

YJIT: New experimental in-process JIT compiler

Ruby 3.1 merges YJIT, a new in-process JIT compiler developed by Shopify.

Since Ruby 2.6 introduced MJIT in 2018, its performance greatly improved, and finally we achieved Ruby3x3 last year. But even though Optcarrot has shown impressive speedups, the JIT hasn’t benefited real world business applications.

Recently Shopify contributed many Ruby improvements to speed up their Rails application. YJIT is an important contribution, and aims to improve the performance of Rails applications.

Though MJIT is a method-based JIT compiler and uses an external C compiler, YJIT uses Basic Block Versioning and includes JIT compiler inside it. With Lazy Basic Block Versioning (LBBV) it first compiles the beginning of a method, and incrementally compiles the rest when the type of arguments and variables are dynamically determined. See YJIT: a basic block versioning JIT compiler for CRuby for a detailed introduction.

With this technology, YJIT achieves both fast warmup time and performance improvements on most real-world software, up to 22% on railsbench, 39% on liquid-render.

YJIT is still an experimental feature, and as such, it is disabled by default. If you want to use this, specify the --yjit command-line option to enable YJIT. It is also limited to macOS & Linux on x86-64 platforms for now.

debug gem: A new debugger

A new debugger debug.gem is bundled. debug.gem is fast debugger implementation and it provides many features like remote debugging, colorful REPL, IDE (VSCode) integration and more. It replaces lib/debug.rb standard library.

error_highlight: Fine-grained error location in backtrace

A built-in gem, error_highlight, has been introduced. It includes fine-grained error location in backtrace:

$ ruby test.rb
test.rb:1:in `<main>': undefined method `time' for 1:Integer (NoMethodError)

1.time {}
Did you mean?  times

This gem is enabled by default. You can disable it by using a command-line option --disable-error_highlight. See the repository in detail.

Irb improvement

To be described in next preview.

Other Notable New Features


  • Values in Hash literals and keyword arguments can be omitted. [Feature #14579]
    • {x:, y:} is a syntax sugar of {x: x, y: y}.
    • foo(x:, y:) is a syntax sugar of foo(x: x, y: y).
  • Pin operator in pattern matching now takes an expression. [Feature #17411]
Prime.each_cons(2).lazy.find_all{_1 in [n, ^(n + 2)]}.take(3).to_a
#=> [[3, 5], [5, 7], [11, 13]]


RBS is a language to describe the structure of Ruby programs. See the repository for detail.

Updates since Ruby 3.0.0:

  • rbs collection has been introduced to manage gems’ RBSs. doc
  • Many signatures for built-in and standard libraries have been added/updated.
  • It includes many bug fixes and performance improvements too.

See the for more information.


TypeProf is a static type analyzer for Ruby. It generates a prototype of RBS from non-type-annotated Ruby code. See the document for detail.

Updates since Ruby 3.0.0:

Performance improvements

  • MJIT
    • For workloads like Rails, the default --jit-max-cache is changed from 100 to 10000. The JIT compiler no longer skips compilation of methods longer than 1000 instructions.
    • To support Zeitwerk of Rails, JIT-ed code is no longer cancelled when a TracePoint for class events is enabled.

Other notable changes since 3.0

  • One-line pattern matching, e.g., ary => [x, y, z], is no longer experimental.
  • Multiple assignment evaluation order has been changed slightly. [Bug #4443]
    • foo[0], bar[0] = baz, qux was evaluated in order baz, qux, foo, and then bar in Ruby 3.0. In Ruby 3.1, it is evaluated in order foo, bar, baz, and then qux.
  • Variable Width Allocation: Strings (experimental) [Bug #18239]

Standard libraries updates

  • Some standard libraries are updated.
    • RubyGems
    • Bundler
    • RDoc 6.4.0
    • ReLine
    • JSON 2.6.0
    • Psych 4.0.2
    • FileUtils 1.6.0
    • Fiddle
    • StringIO 3.0.1
    • IO::Console 0.5.9
    • IO::Wait 0.2.0
    • CSV
    • Etc 1.3.0
    • Date 3.2.0
    • Zlib 2.1.1
    • StringScanner
    • IpAddr
    • Logger 1.4.4
    • OStruct 0.5.0
    • Irb
    • Racc 1.6.0
    • Delegate 0.2.0
    • Benchmark 0.2.0
    • CGI 0.3.0
    • Readline(C-ext) 0.1.3
    • Timeout 0.2.0
    • YAML 0.2.0
    • URI 0.11.0
    • OpenSSL
    • DidYouMean
    • Weakref 0.1.1
    • Tempfile 0.1.2
    • TmpDir 0.1.2
    • English 0.7.1
    • Net::Protocol 0.1.2
    • Net::Http 0.2.0
    • BigDecimal
    • OptionParser 0.2.0
    • Set
    • Find 0.1.1
    • Rinda 0.1.1
    • Erb
    • NKF 0.1.1
    • Base64 0.1.1
    • OpenUri 0.2.0
    • SecureRandom 0.1.1
    • Resolv 0.2.1
    • Resolv::Replace 0.1.0
    • Time 0.2.0
    • PP 0.2.1
    • Prettyprint 0.1.1
    • Drb 2.1.0
    • Pathname 0.2.0
    • Digest 3.1.0.pre2
    • Un 0.2.0
  • The following bundled gems are updated.
    • minitest 5.14.4
    • power_assert 2.0.1
    • rake 13.0.6
    • test-unit 3.5.0
    • rbs 1.6.2
    • typeprof 0.20.0
  • The following default gems are now bundled gems.
    • net-ftp
    • net-imap
    • net-pop
    • net-smtp
    • matrix
    • prime

See NEWS or commit logs for more details.

With those changes, 2963 files changed, 529321 insertions(+), 92305 deletions(-) since Ruby 3.0.0!



    SIZE: 20821221
    SHA1: 40dfd3db076a49fab9a0eee51e89d9b3d16a4e23
    SHA256: 540f49f4c3aceb1a5d7fb0b8522a04dd96bc4a22f9660a6b59629886c8e010d4
    SHA512: 63f528f20905827d03649ed9804e4a4e5c15078f9c6c8efcfb306baa7baafa17a406eb09a2c08b42e151e14af33b1aadbd9fb1cc84f9353d070b54bbf1ff950d

    SIZE: 15742844
    SHA1: 22aa861b17031cd1b163b7443f5f2f5897c5895e
    SHA256: 86a836ad42f6a7a469fce71ffec48fd3184af55bf79e488b568a4f64adee551d
    SHA512: bdbd7c624197ca478658280d84123a8c12ae72425bc566dcc75989c5b5ef114dd57e64efc09e2413ed615d9b47621a70ace0f3612e8ca7ba853822ad9e88c0b0

    SIZE: 25019629
    SHA1: ef5fa22890e55935db4b96b3089a8aea1335bd85
    SHA256: 4e8d118b2365164873148ac545a8fa36c098b846a9b19ebb9037f8ee9adb4414
    SHA512: 917803aac0848e00871614a09740b5c9cca26f200d68580dde61666633f1b7fee506e25ea4ed0c38eb20149417bf9f1ed449a4d2aec5b726de670e7177e5c07a

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.