[ruby-core:96466] Ruby 2.7.0 Released

We are pleased to announce the release of Ruby 2.7.0.

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]](https://bugs.ruby-lang.org/issues/14912)

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

```ruby
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](https://speakerdeck.com/k_tsj/pattern-matching-new-feature-in-ruby-2-dot-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 pure Ruby implementation.
It also provides rdoc integration. In `irb` you can display the reference
for a given class, module, or method.
[[Feature #14683]](https://bugs.ruby-lang.org/issues/14683),
[[Feature #14787]](https://bugs.ruby-lang.org/issues/14787),
[[Feature #14918]](https://bugs.ruby-lang.org/issues/14918)

Besides, source lines shown at `binding.irb` and inspect results
for core-class objects are now colorized.

<video autoplay="autoplay" controls="controls" muted="muted"
width="576" height="259"
poster="https://cache.ruby-lang.org/pub/media/irb-reline-screenshot.png">
  <source src="https://cache.ruby-lang.org/pub/media/irb_improved_with_key_take2.mp4"
type="video/mp4">
</video>

## 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 friendly.
[[Feature #15626]](https://bugs.ruby-lang.org/issues/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]](https://bugs.ruby-lang.org/issues/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.

  ```ruby
  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.

  ```ruby
  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.

  ```ruby
  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.

  ```ruby
  def foo(opt={});  end; foo( key: 42 )   # OK
  ```

* Non-symbols are allowed as keyword argument keys if the method accepts
  arbitrary keywords.
  [[Feature #14183]](https://bugs.ruby-lang.org/issues/14183)

  ```ruby
  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]](https://bugs.ruby-lang.org/issues/14183)

  ```ruby
  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]](https://bugs.ruby-lang.org/issues/14183)

  ```ruby
  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 incompatibility
have been pointed out to be too verbose.  Currently, two possible solutions
are discussed; disabling deprecation warnings by default
([#16345](https://bugs.ruby-lang.org/issues/16345))
or suppressing duplicated warnings
([#16289](https://bugs.ruby-lang.org/issues/16289)).
The final decision is not made, but will be fixed by the official release.

## Other Notable New Features

* Numbered parameter as the default block parameter is introduced.
  [[Feature #4475]](https://bugs.ruby-lang.org/issues/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]](https://bugs.ruby-lang.org/issues/14799)

  ```ruby
  ary[..3]  # identical to ary[0..3]
  rel.where(sales: ..100)
  ```

* `Enumerable#tally` is added.  It counts the occurrence of each element.

  ```ruby
  ["a", "b", "c", "b"].tally
  #=> {"a"=>1, "b"=>2, "c"=>1}
  ```

* Calling a private method on `self` is now allowed.
  [[Feature #11297]](https://bugs.ruby-lang.org/issues/11297),
  [[Feature #16123]](https://bugs.ruby-lang.org/issues/16123)

  ```ruby
  def foo
  end
  private :foo
  self.foo
  ```

* `Enumerator::Lazy#eager` is added.
  It generates a non-lazy enumerator from a lazy enumerator.
  [[Feature #15901]](https://bugs.ruby-lang.org/issues/15901)

  ```ruby
  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.

* Fiber's cache strategy is changed and fiber creation is speed up.
  [GH-2224](https://github.com/ruby/ruby/pull/2224)

* `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]](https://bugs.ruby-lang.org/issues/16150)

* The performance of `CGI.escapeHTML` is improved.
  [GH-2226](https://github.com/ruby/ruby/pull/2226)

* The performance of Monitor and MonitorMixin is improved.
  [[Feature #16255]](https://bugs.ruby-lang.org/issues/16255)

* Per-call-site method cache, which has been there since around 1.9, was
  improved: cache hit rate raised from 89% to 94%.
  See [GH-2583](https://github.com/ruby/ruby/pull/2583)

* RubyVM::InstructionSequence#to_binary method generates compiled
binary. The binary size is reduced. [Feature #16163]

## Other notable changes since 2.6

* Some standard libraries are updated.
  * Bundler 2.1.2
    ([Release note](https://github.com/bundler/bundler/releases/tag/v2.1.2)
  * RubyGems 3.1.2
    * ([Release note for
3.1.0](https://github.com/rubygems/rubygems/releases/tag/v3.1.0)
    * ([Release note for
3.1.1](https://github.com/rubygems/rubygems/releases/tag/v3.1.1)
    * ([Release note for
3.1.2](https://github.com/rubygems/rubygems/releases/tag/v3.1.2)
  * Racc 1.4.15
  * CSV 3.1.2
    ([NEWS](https://github.com/ruby/csv/blob/v3.1.2/NEWS.md))
  * REXML 3.2.3
    ([NEWS](https://github.com/ruby/rexml/blob/v3.2.3/NEWS.md))
  * RSS 0.2.8
    ([NEWS](https://github.com/ruby/rss/blob/v0.2.8/NEWS.md))
  * StringScanner 1.0.3
  * Some other libraries that have no original version are also updated.

* The following libraries are no longer bundled gems.
  Install corresponding gems to use these features.
  * CMath (cmath gem)
  * Scanf (scanf gem)
  * Shell (shell gem)
  * Synchronizer (sync gem)
  * ThreadsWait (thwait gem)
  * E2MM (e2mmap gem)

* `profile.rb` was removed from standard library.

* 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 errs.

* Update Unicode version and Emoji version from 11.0.0 to 12.0.0.
  [[Feature #15321]](https://bugs.ruby-lang.org/issues/15321)

* Update Unicode version to 12.1.0,
  adding support for U+32FF SQUARE ERA NAME REIWA.
  [[Feature #15195]](https://bugs.ruby-lang.org/issues/15195)

* `Date.jisx0301`, `Date#jisx0301`, and `Date.parse` support the
  new Japanese era.
  [[Feature #15742]](https://bugs.ruby-lang.org/issues/15742)

* Require compilers to support C99
  [[Misc #15347]](https://bugs.ruby-lang.org/issues/15347)
  * Details of our dialect:
    <https://bugs.ruby-lang.org/projects/ruby-trunk/wiki/C99>

See [NEWS](https://github.com/ruby/ruby/blob/v2_7_0/NEWS)
or [commit logs](https://github.com/ruby/ruby/compare/v2_6_0...v2_7_0)
for more details.


With those changes, [4190 files changed, 227498 insertions(+), 99979
deletions(-)](https://github.com/ruby/ruby/compare/v2_6_0...v2_7_0)
since Ruby 2.6.0!

Merry Christmas, Happy Holidays, and enjoy programming with Ruby 2.7!

## Download

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## 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.

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