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 Allow disabling ENV write-through to the real environment [JRUBY-5934] #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