NEWS for Ruby 3.0.0 ↑

This document is a list of user visible feature changes since the 2.7.0 release, except for bug fixes.

Note that each entry is kept to a minimum, see links for details.

Language changes ↑

  • Keyword arguments are now separated from positional arguments. Code that resulted in deprecation warnings in Ruby 2.7 will now result in ArgumentError or different behavior. [Feature #14183]

  • Procs accepting a single rest argument and keywords are no longer subject to autosplatting. This now matches the behavior of Procs accepting a single rest argument and no keywords. [Feature #16166]

    pr = proc{|*a, **kw| [a, kw]}

pr.call([1])
# 2.7 => [[1], {}]
# 3.0 => [[[1]], {}]

pr.call([1, {a: 1}])
# 2.7 => [[1], {:a=>1}] # and deprecation warning
# 3.0 => [[[1, {:a=>1}]], {}]

  • Arguments forwarding (...) now supports leading arguments. [Feature #16378]

    def method_missing(meth, ...)
  send(:"do_#{meth}", ...)
end

  • Pattern matching (case/in) is no longer experimental. [Feature #17260]

  • One-line pattern matching is redesigned. [EXPERIMENTAL]

    • => is added. It can be used like a rightward assignment. [Feature #17260]

      0 => a
p a #=> 0

{b: 0, c: 1} => {b:}
p b #=> 0

    • in is changed to return true or false. [Feature #17371]

      # version 3.0
0 in 1 #=> false

# version 2.7
0 in 1 #=> raise NoMatchingPatternError

  • Find-pattern is added. [EXPERIMENTAL] [Feature #16828]

    case ["a", 1, "b", "c", 2, "d", "e", "f", 3]
in [*pre, String => x, String => y, *post]
  p pre  #=> ["a", 1]
  p x    #=> "b"
  p y    #=> "c"
  p post #=> [2, "d", "e", "f", 3]
end

  • Endless method definition is added. [EXPERIMENTAL] [Feature #16746]

    def square(x) = x * x

  • Interpolated String literals are no longer frozen when # frozen-string-literal: true is used. [Feature #17104]

  • Magic comment shareable_constant_value added to freeze constants. See Magic Comments for more details. [Feature #17273]

  • A static analysis foundation is introduced.

    • RBS is introduced. It is a type definition language for Ruby programs.

    • TypeProf is experimentally bundled. It is a type analysis tool for Ruby programs.

  • Deprecation warnings are no longer shown by default (since Ruby 2.7.2). Turn them on with -W:deprecated (or with -w to show other warnings too). [Feature #16345]

  • $SAFE and $KCODE are now normal global variables with no special behavior. C-API methods related to $SAFE have been removed. [Feature #16131] [Feature #17136]

  • yield in singleton class definitions in methods is now a SyntaxError instead of a warning. yield in a class definition outside of a method is now a SyntaxError instead of a LocalJumpError. [Feature #15575]

  • When a class variable is overtaken by the same definition in an ancestor class/module, a RuntimeError is now raised (previously, it only issued a warning in verbose mode). Additionally, accessing a class variable from the toplevel scope is now a RuntimeError. [Bug #14541]

  • Assigning to a numbered parameter is now a SyntaxError instead of a warning.

Command line options ↑

--help option ↑

When the environment variable RUBY_PAGER or PAGER is present and has a non-empty value, and the standard input and output are tty, the --help option shows the help message via the pager designated by the value. [Feature #16754]

--backtrace-limit option ↑

The --backtrace-limit option limits the maximum length of a backtrace. [Feature #8661]

Core classes updates ↑

Outstanding ones only.

Stdlib updates ↑

Outstanding ones only.

Compatibility issues ↑

Excluding feature bug fixes.

Stdlib compatibility issues ↑

  • Default gems

    • The following libraries are promoted to default gems from stdlib.

      • English

      • abbrev

      • base64

      • drb

      • debug

      • erb

      • find

      • net-ftp

      • net-http

      • net-imap

      • net-protocol

      • open-uri

      • optparse

      • pp

      • prettyprint

      • resolv-replace

      • resolv

      • rinda

      • set

      • securerandom

      • shellwords

      • tempfile

      • tmpdir

      • time

      • tsort

      • un

      • weakref

    • The following extensions are promoted to default gems from stdlib.

      • digest

      • io-nonblock

      • io-wait

      • nkf

      • pathname

      • syslog

      • win32ole

  • Bundled gems

  • SDBM has been removed from the Ruby standard library. [Bug #8446]

  • WEBrick has been removed from the Ruby standard library. [Feature #17303]

C API updates ↑

  • C API functions related to $SAFE have been removed. [Feature #16131]

  • C API header file ruby/ruby.h was split. [GH-2991]

    This should have no impact on extension libraries, but users might experience slow compilations.

  • Memory view interface [EXPERIMENTAL]

    • The memory view interface is a C-API set to exchange a raw memory area, such as a numeric array or a bitmap image, between extension libraries. The extension libraries can share also the metadata of the memory area that consists of the shape, the element format, and so on. Using these kinds of metadata, the extension libraries can share even a multidimensional array appropriately. This feature is designed by referring to Python’s buffer protocol. [Feature #13767] [Feature #14722]

  • Ractor related C APIs are introduced (experimental) in “include/ruby/ractor.h”.

Implementation improvements ↑

  • New method cache mechanism for Ractor. [Feature #16614]

    • Inline method caches pointed from ISeq can be accessed by multiple Ractors in parallel and synchronization is needed even for method caches. However, such synchronization can be overhead so introducing new inline method cache mechanisms, (1) Disposable inline method cache (2) per-Class method cache and (3) new invalidation mechanism. (1) can avoid per-method call synchronization because it only uses atomic operations. See the ticket for more details.

  • The number of hashes allocated when using a keyword splat in a method call has been reduced to a maximum of 1, and passing a keyword splat to a method that accepts specific keywords does not allocate a hash.

  • super is optimized when the same type of method is called in the previous call if it’s not refinements or an attr reader or writer.

JIT ↑

  • Performance improvements of JIT-ed code

    • Microarchitectural optimizations

      • Native functions shared by multiple methods are deduplicated on JIT compaction.

      • Decrease code size of hot paths by some optimizations and partitioning cold paths.

    • Instance variables

      • Eliminate some redundant checks.

      • Skip checking a class and a object multiple times in a method when possible.

      • Optimize accesses in some core classes like Hash and their subclasses.

    • Method inlining support for some C methods

      • Kernel: #class, #frozen?

      • Integer: #-@, #~, #abs, #bit_length, #even?, #integer?, #magnitude, #odd?, #ord, #to_i, #to_int, #zero?

      • Struct: reader methods for 10th or later members

    • Constant references are inlined.

    • Always generate appropriate code for ==, nil?, and ! calls depending on a receiver class.

    • Reduce the number of PC accesses on branches and method returns.

    • Optimize C method calls a little.

  • Compilation process improvements

    • It does not keep temporary files in /tmp anymore.

    • Throttle GC and compaction of JIT-ed code.

    • Avoid GC-ing JIT-ed code when not necessary.

    • GC-ing JIT-ed code is executed in a background thread.

    • Reduce the number of locks between Ruby and JIT threads.

Static analysis ↑

RBS ↑

  • RBS is a new language for type definition of Ruby programs. It allows writing types of classes and modules with advanced types including union types, overloading, generics, and interface types for duck typing.

  • Ruby ships with type definitions for core/stdlib classes.

  • rbs gem is bundled to load and process RBS files.

TypeProf ↑

  • TypeProf is a type analysis tool for Ruby code based on abstract interpretation.

    • It reads non-annotated Ruby code, tries inferring its type signature, and prints the analysis result in RBS format.

    • Though it supports only a subset of the Ruby language yet, we will continuously improve the coverage of language features, analysis performance, and usability.

# test.rb
def foo(x)
  if x > 10
    x.to_s
  else
    nil
  end
end

foo(42)

$ typeprof test.rb
# Classes
class Object
  def foo : (Integer) -> String?
end

Miscellaneous changes ↑

  • Methods using ruby2_keywords will no longer keep empty keyword splats, those are now removed just as they are for methods not using ruby2_keywords.

  • When an exception is caught in the default handler, the error message and backtrace are printed in order from the innermost. [Feature #8661]

  • Accessing an uninitialized instance variable no longer emits a warning in verbose mode. [Feature #17055]