Posted by naruse on 22 Oct 2019

We are pleased to announce the release of Ruby 2.7.0-preview2.

A preview version is released to gather feedback for the final release planned to release on December. It introduces a number of new features and performance improvements, most notably:

Compaction GC

Pattern Matching

REPL improvement

Separation of positional and keyword arguments

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]

Pattern Matching [Experimental]

Pattern matching, 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.

case JSON . parse ( '{...}' , symbolize_names: true ) in { name: "Alice" , children: [{ name: "Bob" , age: age }]} p age ... end

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

REPL improvement

irb , bundled interactive environment (REPL; Read-Eval-Print-Loop), now supports multi-line editing. It’s powered by reline , 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], [Feature #14787], [Feature #14918] Besides, source lines shown at binding.irb and inspect results for core-class objects are now colorized.

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 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 a keyword argument keys if 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 ) # {}

Other Notable New Features

A method reference operator, .: , is introduced as an experimental feature. [Feature #12125], [Feature #13581]

Numbered parameter as the default block parameter is 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 purpose. [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}

Calling a private method on self is now allowed. [Feature #11297] [Feature #16123] 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. Default value of --jit-min-calls is changed from 5 to 10,000 Default value of --jit-max-cache is changed from 1,000 to 100

Symbol#to_s , 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

Other notable changes since 2.6

Some standard libraries are updated. Bundler 2.1.0.pre.1 RubyGems 3.1.0.pre.1 CSV 3.1.2 (NEWS) Racc 1.4.15 REXML 3.2.3 (NEWS) RSS 0.2.8 (NEWS) StringScanner 1.0.3 Some of other libraries that have no original version are also updated.

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]

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] Details of our dialect: https://bugs.ruby-lang.org/projects/ruby-master/wiki/C99



See NEWS or commit logs for more details.

With those changes, 3670 files changed, 201242 insertions(+), 88066 deletions(-) since Ruby 2.6.0!

Enjoy programming with Ruby 2.7!

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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.