Ruby 2.4 support

[headius]

This bug will track all NEWS items new in Ruby 2.4. This list is based off https://github.com/ruby/ruby/blob/trunk/NEWS.

Only changes relevant to JRuby are listed here. MRI-specific internal changes and features are not included.

NOTE: Pull requests should be done against the ruby-2.4 branch.

Language changes

• Multiple assignment in conditional expression is now allowed. Feature #10617

• Refinements is enabled at method by Symbol#to_proc. Feature #9451

• Refinements is enabled with Kernel#send and BasicObject#__send__. Feature #11476

• Rescue modifier now applicable to method arguments. Feature #12686

• Toplevel return is now allowed. Feature #4840

Core classes updates (outstanding ones only)

• Array

  • Array#max and Array#min. Feature #12172

  • Array#sum Feature #12217

  • Array#concat Feature #12333

  • Array#pack now takes optional argument buffer: to reuse an already-allocated buffer. Feature #12217

• Comparable

  • Comparable#clamp. Feature #10594

• Dir

  • Dir.empty?. Feature #10121

• Enumerable

  • Enumerable#sum Feature #12217
  • Enumerable#uniq Feature #11090
  • Enumerable#chunk called without a block now return an Enumerator. Feature #2172

• Enumerator::Lazy

  • Enumerator::Lazy#chunk_while GH-1186
  • Enumerator::Lazy#uniq Feature #11090

• File

  • File.empty?. Feature #9969

• Float

  • Float#ceil, Float#floor, and Float#truncate now take an optional digits, as well as Float#round. Feature #12245

  • Float#round now takes an optional keyword argument, half option, and
    the default behavior is round-up. Bug #12548 Bug #12958
    half option can be one of :even, :up, and :down. Feature #12953

• Hash

  • Hash#transform_values and Hash#transform_values! Feature #12512
  • Hash#compact and Hash#compact! Feature #11818

• Integer

  • Integer#ceil, Integer#floor, and Integer#truncate now take an optional digits, as well as Integer#round. Feature #12245

  • Fixnum and Bignum are unified into Integer Feature #12005

  • Integer#digits for extracting columns of place-value notation Feature #12447

  • Integer#round now takes an optional keyword argument, half option, and
    the default behavior is round-up. Bug #12548 Bug #12958
    half option can be one of :even, :up, and :down. Feature #12953

• IO

  • IO#gets, IO#readline, IO#each_line, IO#readlines, IO.foreach now takes an optional keyword argument, chomp flag. Feature #12553

• Kernel

  • Kernel#clone now takes an optional keyword argument, freeze flag. Feature #12300

• MatchData

  • MatchData#named_captures Feature #11999
  • MatchData#values_at supports named captures Feature #9179

• Module

  • Module.used_modules Feature #7418
  • Module#refine accepts a module as the argument now. Feature #12534

• Numeric

  • Numeric#finite?, Numeric#infinite? Feature #12039

• Process

  • Support CLOCK_MONOTONIC_RAW_APPROX, CLOCK_UPTIME_RAW, and CLOCK_UPTIME_RAW_APPROX which are introduced by macOS 10.12.

• Rational

  • Rational#round now takes an optional keyword argument, half option, and
    the default behavior is round-up. Bug #12548 Bug #12958
    half option can be one of :even, :up, and :down. Feature #12953

• Regexp

  • Regexp#match? Feature #8110
  • meta character \X matches Unicode 9.0 characters with some workarounds for UTR #51 Unicode Emoki, Version 4.0 emoji zwj sequences
  • Update Onigmo 6.0.0 (we have never incorporated all of Onigmo's additions into Joni)

• Regexp/String: Updated Unicode version from 8.0.0 to 9.0.0 Feature #12513

• String

  • String#upcase, String#downcase, String#capitalize, String#swapcase and their bang variants work for all of Unicode, and are no longer limited to ASCII. Supported encodings are UTF-8, UTF-16BE/LE, UTF-32BE/LE, and ISO-8859-1~16. Variations are available with options. See the documentation of String#downcase for details. Feature #10085

  • String.new(capacity: size) Feature #12024

  • String#concat, String#prepend Feature #12333 Now takes multiple arguments.

  • String#unpack1 Feature #12752

  • String#match? Feature #12898

  • String#each_line, String#lines now takes an optional keyword argument, chomp flag. Feature #12553

  • String#concat, String#prepend now take multiple arguments Feature #12333

  • String#casecmp? Feature #12786

• StringIO

  • StringIO#gets, StringIO#readline, StringIO#each_line, StringIO#readlines now take optional keyword argument, chomp flag. Feature #12553

• Symbol

  • Symbol#match now returns MatchData. Bug #11991

  • Symbol#upcase, Symbol#downcase, Symbol#capitalize, and Symbol#swapcase now work for all of Unicode. See the documentation of String#downcase for details. Feature #10085

  • Symbol#match? Feature #12898

  • Symbol#casecmp? Feature #12786

• Thread

  • Thread#report_on_exception and Thread.report_on_exception Feature #6647

• TracePoint

  • TracePoint#callee_id Feature #12747

• Warning

  • New module named Warning is introduced. By default it has only one singleton method, named warn. This makes it possible for 3rd-party libraries to control the way warnings are handled. Feature #12299

Stdlib updates (only items that need specific attention in JRuby)

• pathname

  • New method: Pathname#empty? Feature #12596

• Readline

  • Readline.quoting_detection_proc and Readline.quoting_detection_proc= Feature #12659

Compatibility issues (excluding feature bug fixes)

• Array#sum and Enumerable#sum are implemented. Feature #12217

• Fixnum and Bignum are unified into Integer Feature #12005

• String/Symbol#upcase/downcase/swapcase/capitalize(!) now work for all of Unicode, not only for ASCII. Feature #10085

• TRUE / FALSE / NIL These constants are now obsoleted. Feature #12574

Stdlib compatibility issues (excluding feature bug fixes)

• DateTime

  • DateTime#to_time now preserves timezone. Bug #12189

• Psych

  • Update Psych 2.2.2

• RDoc

  • Update RDoc 5.0.0

• RubyGems

  • Update RubyGems 2.6.8

• Time

  • Time#to_time now preserves timezone. Bug #12271

• thread

  • the extension library is removed. Till 2.0 it was a pure ruby script "thread.rb", which has precedence over "thread.so", and has been provided in $LOADED_FEATURES since 2.1.

• Zlib

  • Zlib.gzip and Zlib.gunzip Feature #13020

Implementation improvements

• In some condition, [x, y].max and [x, y].min are optimized so that a temporal array is not created. The concrete condition is an implementation detail: currently, the array literal must have no splat, must have at least one expression but literal, the length must be <= 0x100, and Array#max and min must not be redefined. It will work in most casual and real-life use case where it is written with intent to Math.max(x, y).

• Thread deadlock detection now shows their backtrace and dependency. Feature #8214

• st_table (st.c) internal data structure is improved. Feature #12142

• Rational is extensively optimized. Feature #12484

[ianks]

Which of these should be implemented in ruby?

[headius]

@ianks Any that make sense! Obviously some things, like potential Hash optimizations, would have to be in Java, but many of these features would be just fine in Ruby. See https://github.com/jruby/jruby/tree/master/core/src/main/ruby/jruby/kernel.

[headius]

Note that for [x, y].max, JRuby 9.1.5.0+ already allocates a smaller object to hold x, y. Remaining work would be enhancements to the IR builder to optimize this structure to just do the comparison.

[headius]

Unless there are late-breaking additions, I think this is what we're settling on for 2.4 support in the initial JRuby 9.2 release. We'll continue to track missing 2.4 features at #4687 and related issues.