Ruby 2.7.0-rc2 Released

We are pleased to announce the release of Ruby 2.7.0-rc2.

A release candidate is released to gather feedback for the final release planned for December 25.

It also introduces a number of new features and performance improvements, most notably:

  • Pattern Matching
  • REPL improvement
  • Compaction GC
  • Separation of positional and keyword arguments

Pattern Matching [Experimental]

Pattern matching, a widely used feature in functional programming languages, is introduced as an experimental feature. [Feature #14912]

It can traverse a given object and assign its value if it matches a pattern.

require "json"

json = <<END
{
  "name": "Alice",
  "age": 30,
  "children": [{ "name": "Bob", "age": 2 }]
}
END

case JSON.parse(json, symbolize_names: true)
in {name: "Alice", children: [{name: "Bob", age: age}]}
  p age #=> 2
end

For more details, please see Pattern matching - New feature in Ruby 2.7.

REPL improvement

irb, the bundled interactive environment (REPL; Read-Eval-Print-Loop), now supports multi-line editing. It is powered by reline, a readline-compatible library implemented in pure Ruby. It also provides rdoc integration. In irb you can display the reference for a given class, module, or method. [Feature #14683], [Feature #14787], [Feature #14918]

Besides, source lines shown by Binding#irb and inspect results for core-class objects are now colorized.

Compaction GC

This release introduces Compaction GC which can defragment a fragmented memory space.

Some multi-threaded Ruby programs may cause memory fragmentation, leading to high memory usage and degraded speed.

The GC.compact method is introduced for compacting the heap. This function compacts live objects in the heap so that fewer pages may be used, and the heap may be more CoW (copy-on-write) friendly. [Feature #15626]

Separation of positional and keyword arguments

Automatic conversion of keyword arguments and positional arguments is deprecated, and conversion will be removed in Ruby 3. [Feature #14183]

  • When a method call passes a Hash at the last argument, and when it passes no keywords, and when the called method accepts keywords, a warning is emitted. To continue treating the hash as keywords, add a double splat operator to avoid the warning and ensure correct behavior in Ruby 3.
  def foo(key: 42); end; foo({key: 42})   # warned
  def foo(**kw);    end; foo({key: 42})   # warned
  def foo(key: 42); end; foo(**{key: 42}) # OK
  def foo(**kw);    end; foo(**{key: 42}) # OK
  
  • When a method call passes keywords to a method that accepts keywords, but it does not pass enough required positional arguments, the keywords are treated as a final required positional argument, and a warning is emitted. Pass the argument as a hash instead of keywords to avoid the warning and ensure correct behavior in Ruby 3.
  def foo(h, **kw); end; foo(key: 42)      # warned
  def foo(h, key: 42); end; foo(key: 42)   # warned
  def foo(h, **kw); end; foo({key: 42})    # OK
  def foo(h, key: 42); end; foo({key: 42}) # OK
  
  • When a method accepts specific keywords but not a keyword splat, and a hash or keywords splat is passed to the method that includes both Symbol and non-Symbol keys, the hash will continue to be split, and a warning will be emitted. You will need to update the calling code to pass separate hashes to ensure correct behavior in Ruby 3.
  def foo(h={}, key: 42); end; foo("key" => 43, key: 42)   # warned
  def foo(h={}, key: 42); end; foo({"key" => 43, key: 42}) # warned
  def foo(h={}, key: 42); end; foo({"key" => 43}, key: 42) # OK
  
  • If a method does not accept keywords, and is called with keywords, the keywords are still treated as a positional hash, with no warning. This behavior will continue to work in Ruby 3.
  def foo(opt={});  end; foo( key: 42 )   # OK
  
  • Non-symbols are allowed as keyword argument keys if the method accepts arbitrary keywords. [Feature #14183]
  def foo(**kw); p kw; end; foo("str" => 1) #=> {"str"=>1}
  
  • **nil is allowed in method definitions to explicitly mark that the method accepts no keywords. Calling such a method with keywords will result in an ArgumentError. [Feature #14183]
  def foo(h, **nil); end; foo(key: 1)       # ArgumentError
  def foo(h, **nil); end; foo(**{key: 1})   # ArgumentError
  def foo(h, **nil); end; foo("str" => 1)   # ArgumentError
  def foo(h, **nil); end; foo({key: 1})     # OK
  def foo(h, **nil); end; foo({"str" => 1}) # OK
  
  • Passing an empty keyword splat to a method that does not accept keywords no longer passes an empty hash, unless the empty hash is necessary for a required parameter, in which case a warning will be emitted. Remove the double splat to continue passing a positional hash. [Feature #14183]
  h = {}; def foo(*a) a end; foo(**h) # []
  h = {}; def foo(a) a end; foo(**h)  # {} and warning
  h = {}; def foo(*a) a end; foo(h)   # [{}]
  h = {}; def foo(a) a end; foo(h)    # {}
  

NOTE: Too many deprecation warnings about keyword argument incompatibilities have been pointed out to be too verbose. Currently, two possible solutions are discussed; disabling deprecation warnings by default (#16345) or suppressing duplicated warnings (#16289). The final decision is not made, but will be fixed by the official release.

Other Notable New Features

  • A method reference operator, .:, was introduced as an experimental feature in earlier previews, but was reverted. [Feature #12125], [Feature #13581], [Feature #16275]

  • Numbered parameters as default block parameters are introduced as an experimental feature. [Feature #4475]

  • A beginless range is experimentally introduced. It might not be as useful as an endless range, but would be good for DSL purposes. [Feature #14799]

  ary[..3]  # identical to ary[0..3]
  rel.where(sales: ..100)
  
  • Enumerable#tally is added. It counts the occurrence of each element.
  ["a", "b", "c", "b"].tally
  #=> {"a"=>1, "b"=>2, "c"=>1}
  
  def foo
  end
  private :foo
  self.foo
  
  • Enumerator::Lazy#eager is added. It generates a non-lazy enumerator from a lazy enumerator. [Feature #15901]
  a = %w(foo bar baz)
  e = a.lazy.map {|x| x.upcase }.map {|x| x + "!" }.eager
  p e.class               #=> Enumerator
  p e.map {|x| x + "?" }  #=> ["FOO!?", "BAR!?", "BAZ!?"]
  

Performance improvements

  • JIT [Experimental]

    • JIT-ed code is recompiled to less-optimized code when an optimization assumption is invalidated.

    • Method inlining is performed when a method is considered as pure. This optimization is still experimental and many methods are NOT considered as pure yet.

    • The default value of --jit-min-calls is changed from 5 to 10,000.

    • The default value of --jit-max-cache is changed from 1,000 to 100.

  • Module#name, true.to_s, false.to_s, and nil.to_s now always return a frozen String. The returned String is always the same for a given object. [Experimental] [Feature #16150]

  • The performance of CGI.escapeHTML is improved. GH-2226

  • The performance of Monitor and MonitorMixin is improved. [Feature #16255]

Other notable changes since 2.6

  • Some standard libraries are updated.
    • Bundler 2.1.0.pre.3 (History)
    • RubyGems 3.1.0.pre.3 (History)
    • CSV 3.1.2 (NEWS)
    • Racc 1.4.15
    • REXML 3.2.3 (NEWS)
    • RSS 0.2.8 (NEWS)
    • StringScanner 1.0.3
    • Some other libraries that have no original version are also updated.
  • Promote stdlib to default gems
    • The following default gems were published on rubygems.org
      • benchmark
      • cgi
      • delegate
      • getoptlong
      • net-pop
      • net-smtp
      • open3
      • pstore
      • singleton
    • The following default gems were only promoted at ruby-core, but not yet published on rubygems.org.
      • monitor
      • observer
      • timeout
      • tracer
      • uri
      • yaml
  • Proc.new and proc with no block in a method called with a block is warned now.

  • lambda with no block in a method called with a block raises an exception.

  • Update Unicode version and Emoji version from 11.0.0 to 12.0.0. [Feature #15321]

  • Update Unicode version to 12.1.0, adding support for U+32FF SQUARE ERA NAME REIWA. [Feature #15195]

  • Date.jisx0301, Date#jisx0301, and Date.parse support the new Japanese era. [Feature #15742]

  • Require compilers to support C99. [Misc #15347]

See NEWS or commit logs for more details.

With those changes, 4184 files changed, 226864 insertions(+), 99937 deletions(-) since Ruby 2.6.0! Enjoy programming with Ruby 2.7!

Download

  • https://cache.ruby-lang.org/pub/ruby/2.7/ruby-2.7.0-rc2.tar.bz2

    SIZE: 14686646
    SHA1: e04680f57d8b7576637eb75b8b56aceeb1806992
    SHA256: 8f94ea7ba79b6e95225fb4a7870e882081182c3d12d58c4cad2a7d2e7865cf8e
    SHA512: 9010f72bb3f33b6cd3f515531e6e05198f295bb2a8a788e3a46cdfd776a9f6176b6ba8612f07f0236a11359302d2b77fdecca1dc6be33581edbb028069397a0a
    
  • https://cache.ruby-lang.org/pub/ruby/2.7/ruby-2.7.0-rc2.tar.gz

    SIZE: 16775053
    SHA1: 787a86023f0abe6ca9c0b31e95328725e8bb7814
    SHA256: b16cd92479e5648cc53425602e9dc6d76b18dd2cc180add2fd4c9f254646779d
    SHA512: d59910a140ea1b7ca7a64073dbbe4cbe8f11cd6fc68ea7874ca160e1a23549bd159f49f4d199002f9806e77d4426bff3aa81b62707d539e0710ece7b7ff83438
    
  • https://cache.ruby-lang.org/pub/ruby/2.7/ruby-2.7.0-rc2.tar.xz

    SIZE: 11965624
    SHA1: 1f9f30eaf1829250931c4c465ee1c15e07452e7d
    SHA256: c90d29fba655b2dd577ff755f084e4d1fe0673cfcd888af7ff5d0b2d2f449bb7
    SHA512: dba23aada4921c98eb90d216db656833d1759c4f611d5087e2a0123d932ab1c6704dfedc0d671d2d51b4b3949ff95b6aec012481141c6fce3988a3d0bc5d18b8
    
  • https://cache.ruby-lang.org/pub/ruby/2.7/ruby-2.7.0-rc2.zip

    SIZE: 20642713
    SHA1: e0b6f91398d55436b776d7a5eae0faaf810b1578
    SHA256: ac87c1666cc840cad26083a067bae1975d1fdb41ca1f1569903c05bca1b61174
    SHA512: 4e84b1f59b574a59b5346d30a0770e06ad81a4838813cc8789157f4e1a3fcbe7ca75bf83663c20736024760f1b0675ca288f1cee7f8a28f8918c4e43b0d09982
    

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.