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Nobuyoshi Nakada 175952bf07

NEWS for [Feature #16233 ] [ci skip]

2020-11-22 23:08:38 +09:00

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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 so brief that no reason behind or reference information is supplied with. For a full list of changes with all sufficient information, see the ChangeLog file or Redmine (e.g. https://bugs.ruby-lang.org/issues/$FEATURE_OR_BUG_NUMBER).

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]
Arguments forwarding (...) now supports leading arguments. [Feature #16378]
```
def method_missing(meth, ...)
  send(:"do_#{meth}", ...)
end
```

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}]], {}]

$SAFE is now a normal global variable with no special behavior. C-API methods related to $SAFE have been removed. [Feature #16131]
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]
Pattern matching is no longer experimental. [Feature #17260]

One-line pattern matching now uses => instead of in. [EXPERIMENTAL] [Feature #17260]

# version 3.0
{a: 0, b: 1} => {a:}
p a # => 0

# version 2.7
{a: 0, b: 1} in {a:}
p a # => 0

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

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]
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]
A static analysis foundation is introduced. See "Static analysis" section in detail.
- 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.

Command line options

`--help` option

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

`--backtrace-limit` option

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

Core classes updates

Outstanding ones only.

Array
- Modified methods
  - The following methods now return Array instances instead of subclass instances when called on subclass instances: [Bug #6087]
    - Array#drop
    - Array#drop_while
    - Array#flatten
    - Array#slice!
    - Array#slice/#[]
    - Array#take
    - Array#take_while
    - Array#uniq
    - Array#*
Dir
- Modified method
  - Dir.glob and Dir.[] now sort the results by default, and accept sort: keyword option. [Feature #8709]
ENV
- New method
  - ENV.except, which returns a hash excluding the given keys and their values. [Feature #15822]
Encoding
- New encoding
  - Added new encoding IBM720. [Feature #16233]
Hash
- Modified method
  - Hash#transform_keys now accepts a hash that maps keys to new keys. [Feature #16274]
- New method
  - Hash#except, which returns a hash excluding the given keys and their values. [Feature #15822]
Kernel
- Modified method
  - Kernel#clone when called with freeze: false keyword will call #initialize_clone with the freeze: false keyword. [Bug #14266]
  - Kernel#clone when called with freeze: true keyword will call #initialize_clone with the freeze: true keyword, and will return a frozen copy even if the receiver is unfrozen. [Feature #16175]
  - Kernel#eval when called with two arguments will use "(eval)" for __FILE__ and 1 for __LINE__ in the evaluated code. [Bug #4352]
  - Kernel#lambda now warns if called without a literal block. [Feature #15973]
Module
- Modified method
  - Module#include and #prepend now affect classes and modules that have already included or prepended the receiver, mirroring the behavior if the arguments were included in the receiver before the other modules and classes included or prepended the receiver. [Feature #9573]
```
class C; end
module M1; end
module M2; end
C.include M1
M1.include M2
p C.ancestors #=> [C, M1, M2, Object, Kernel, BasicObject]
```
Thread
- Introduce Fiber.set_scheduler for intercepting blocking operations and Fiber.scheduler for accessing the current scheduler. See doc/scheduler.md for more details. [Feature #16786]
- Fiber.blocking? tells whether the current execution context is blocking. [Feature #16786]
- Thread#join invokes the scheduler hooks block/unblock in a non-blocking execution context. [Feature #16786]
- Thread.ignore_deadlock accessor for disabling the default deadlock detection, allowing the use of signal handlers to break deadlock. [Bug #13768]
Mutex
- Mutex is now acquired per-Fiber instead of per-Thread. This change should be compatible for essentially all usages and avoids blocking when using a scheduler. [Feature #16792]
Fiber
- Fiber.new(blocking: true/false) allows you to create non-blocking execution contexts. [Feature #16786]
- Fiber#blocking? tells whether the fiber is non-blocking. [Feature #16786]
- Fiber#backtrace & Fiber#backtrace_locations provide per-fiber backtrace. [Feature #16815]
- The limitation of Fiber#transfer is relaxed. [Bug #17221]
Kernel
- Kernel.sleep(...) invokes the scheduler hook #kernel_sleep(...) in a non-blocking execution context. [Feature #16786]
IO
- IO#nonblock? now defaults to true. [Feature #16786]
- IO#wait_readable, IO#wait_writable, IO#read, IO#write and other related methods (e.g. #puts, #gets) may invoke the scheduler hook #io_wait(io, events, timeout) in a non-blocking execution context. [Feature #16786]
ConditionVariable
- ConditionVariable#wait may now invoke the block/unblock scheduler hooks in a non-blocking context. [Feature #16786]
Queue / SizedQueue
- Queue#pop, SizedQueue#push and related methods may now invoke the block/unblock scheduler hooks in a non-blocking context. [Feature #16786]
Ractor
- new class to enable parallel execution. See doc/ractor.md for more details.
Symbol
- Modified method
  - Symbol#to_proc now returns a lambda Proc. [Feature #16260]
- New method
  - Symbol#name, which returns the name of the symbol if it is named. The returned string cannot be modified. [Feature #16150]
String
- Modified methods
  - The following methods now return or yield String instances instead of subclass instances when called on subclass instances: [Bug #10845]
    - String#*
    - String#capitalize
    - String#center
    - String#chomp
    - String#chop
    - String#delete
    - String#delete_prefix
    - String#delete_suffix
    - String#downcase
    - String#dump
    - String#each_char
    - String#each_grapheme_cluster
    - String#each_line
    - String#gsub
    - String#ljust
    - String#lstrip
    - String#partition
    - String#reverse
    - String#rjust
    - String#rpartition
    - String#rstrip
    - String#scrub
    - String#slice!
    - String#slice/#[]
    - String#split
    - String#squeeze
    - String#strip
    - String#sub
    - String#succ/#next
    - String#swapcase
    - String#tr
    - String#tr_s
    - String#upcase
Warning
- Modified method
  - Warning#warn now supports a category kwarg. [Feature #17122]
GC
- New method
  - GC.auto_compact=, GC.auto_compact can be used to control when compaction runs. Setting auto_compact= to true will cause compaction to occur during major collections. At the moment, compaction adds significant overhead to major collections, so please test first! [Feature #17176]

Stdlib updates

Outstanding ones only.

RubyGems
- Update to RubyGems 3.2.0.rc.1
Bundler
- Update to Bundler 2.2.0.rc.1
Net::HTTP
- New method
  - Add Net::HTTP#verify_hostname= and Net::HTTP#verify_hostname to skip hostname verification. [Feature #16555]
- Modified method
  - Net::HTTP.get, Net::HTTP.get_response, and Net::HTTP.get_print can take request headers as a Hash in the second argument when the first argument is a URI. [Feature #16686]
IRB
- Update to IRB 1.2.6
OpenStruct
- Initialization no longer lazy [Bug #12136]
- Builtin methods can now be overridden safely. [Bug #15409]
- Implementation uses only methods ending with !.
- Ractor compatible.
- Improved support for YAML [Bug #8382]
- Use officially discouraged. Read "Caveats" section.
Reline
- Update to Reline 0.1.5

Socket

TCPSocket.new now supports resolv_timeout. [Feature #17134]

# it raises SocketError if name resolution is not finished within resolve_timeout.
tcp_socket = TCPSocket.new("example.com", 80, resolv_timeout: 10)

Fiddle
- Update to Fiddle 1.0.2

Compatibility issues

Excluding feature bug fixes.

Regexp literals and all Range objects are frozen [Feature #8948] [Feature #16377] [Feature #15504]
```
/foo/.frozen? #=> true
(42...).frozen? # => true
```
EXPERIMENTAL: Hash#each consistently yields a 2-element array [Bug #12706]
- Now { a: 1 }.each(&->(k, v) { }) raises an ArgumentError due to lambda's arity check.
- This is experimental; if it brings a big incompatibility issue, it may be reverted until 2.8/3.0 release.
When writing to STDOUT redirected to a closed pipe, no broken pipe error message will be shown now. [Feature #14413]
TRUE/FALSE/NIL constants are no longer defined.
Integer#zero? overrides Numeric#zero? for optimization. [Misc #16961]

Stdlib compatibility issues

Default gems
- The following libraries are promoted the 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 the default gems from stdlib.
  - digest
  - io-nonblock
  - io-wait
  - nkf
  - pathname
  - syslog
  - win32ole
Bundled gems
- net-telnet and xmlrpc have been removed from the bundled gems. If you are interested in maintaining them, please comment on your plan to https://github.com/ruby/xmlrpc or https://github.com/ruby/net-telnet.
SDBM have been removed from ruby standard library. [Bug #8446]
- The issues of sdbm will be handled at https://github.com/ruby/sdbm

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] 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 and 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]

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

Native functions shared by multiple methods are deduplicated on JIT compaction.
Decrease code size of hot paths by some optimizations and partitioning cold paths.
Not only pure Ruby methods but also some C methods skip pushing a method frame.
- Kernel#class, Integer#zero?
Always generate appropriate code for ==, nil?, and ! calls depending on a receiver class.
Optimize instance variable access in some core classes like Hash and their subclasses
Eliminate VM register access on a method return
Optimize C method call a little

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, the 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]

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