# NEWS for Ruby 3.1.0 This document is a list of user visible feature changes since the **3.0.0** release, except for bug fixes. Note that each entry is kept to a minimum, see links for details. ## Language changes * The block argument can be now be anonymous, if the block will only be passed to another method. [[Feature #11256]] ```ruby def foo(&) bar(&) end ``` * Pin operator now takes an expression. [[Feature #17411]] ```ruby Prime.each_cons(2).lazy.find_all{_1 in [n, ^(n + 2)]}.take(3).to_a #=> [[3, 5], [5, 7], [11, 13]] ``` * Pin operator now supports instance, class, and global variables. [[Feature #17724]] ```ruby @n = 5 Prime.each_cons(2).lazy.find{_1 in [n, ^@n]} #=> [3, 5] ``` * One-line pattern matching is no longer experimental. * Multiple assignment evaluation order has been made consistent with single assignment evaluation order. With single assignment, Ruby uses a left-to-right evaluation order. With this code: ```ruby foo[0] = bar ``` The following evaluation order is used: 1. `foo` 2. `bar` 3. `[]=` called on the result of `foo` In Ruby before 3.1.0, multiple assignment did not follow this evaluation order. With this code: ```ruby foo[0], bar.baz = a, b ``` Versions of Ruby before 3.1.0 would evaluate in the following order 1. `a` 2. `b` 3. `foo` 4. `[]=` called on the result of `foo` 5. `bar` 6. `baz=` called on the result of `bar` Starting in Ruby 3.1.0, evaluation order is now consistent with single assignment, with the left hand side being evaluated before the right hand side: 1. `foo` 2. `bar` 3. `a` 4. `b` 5. `[]=` called on the result of `foo` 6. `baz=` called on the result of `bar` [[Bug #4443]] * Values in Hash literals and keyword arguments can be omitted. [[Feature #14579]] For example, * `{x:, y:}` is a syntax sugar of `{x: x, y: y}`. * `foo(x:, y:)` is a syntax sugar of `foo(x: x, y: y)`. Constant names, local variable names, and method names are allowed as key names. Note that a reserved word is considered as a local variable or method name even if it's a pseudo variable name such as `self`. * non main-Ractors can get instance variables (ivars) of classes/modules if ivars refer to shareable objects. [[Feature #17592]] ## Command line options ## Core classes updates Outstanding ones only. * Array * Array#intersect? is added. [[Feature #15198]] * Class * Class#descendants, which returns an array of classes directly or indirectly inheriting from the receiver, not including the receiver or singleton classes. [[Feature #14394]] ```ruby class A; end class B < A; end class C < B; end A.descendants #=> [B, C] B.descendants #=> [C] C.descendants #=> [] ``` * Class#subclasses, which returns an array of classes directly inheriting from the receiver, not including singleton classes. [[Feature #18273]] ```ruby class A; end class B < A; end class C < B; end class D < A; end A.subclasses #=> [D, B] B.subclasses #=> [C] C.subclasses #=> [] ``` * Enumerable * Enumerable#compact is added. [[Feature #17312]] * Enumerable#tally now accepts an optional hash to count. [[Feature #17744]] * Enumerable#each_cons and each_slice to return a receiver. [[GH-1509]] ```ruby [1, 2, 3].each_cons(2){} # 3.0 => nil # 3.1 => [1, 2, 3] [1, 2, 3].each_slice(2){} # 3.0 => nil # 3.1 => [1, 2, 3] ``` * Enumerator::Lazy * Enumerator::Lazy#compact is added. [[Feature #17312]] * File * File.dirname now accepts an optional argument for the level to strip path components. [[Feature #12194]] * GC * "GC.measure_total_time = true" enables the measurement of GC. Measurement can introduce overhead. It is enabled by default. GC.measure_total_time returns the current setting. GC.stat[:time] or GC.stat(:time) returns measured time in milli-soconds. * GC.total_time returns measured time in nano-seconds. * Integer * Integer.try_convert is added. [[Feature #15211]] * Kernel * Kernel#load now accepts a module as the second argument, and will load the file using the given module as the top level module. [[Feature #6210]] * MatchData * MatchData#match is added [[Feature #18172]] * MatchData#match_length is added [[Feature #18172]] * Method/UnboundMethod * #public?, #private?, #protected have been added to both Method and UnboundMethod. [[Feature #11689]] * Module * Module#prepend now modifies the ancestor chain if the receiver already includes the argument. Module#prepend still does not modify the ancestor chain if the receiver has already prepended the argument. [[Bug #17423]] * Module#private, #public, #protected, and #module_function will now return their arguments. If a single argument is given, it is returned. If no arguments are given, nil is returned. If multiple arguments are given, they are returned as an array. [[Feature #12495]] * Process * Process.\_fork is added. This is a core method for fork(2). Do not call this method directly; it is called by existing fork methods: Kernel.#fork, Process.fork, and IO.popen("-"). Application monitoring libraries can overwride this method to hook fork event. [[Feature #17795]] * Struct * Passing only keyword arguments to Struct#initialize is warned. You need to use a Hash literal to set a Hash to a first member. [[Feature #16806]] * StructClass#keyword_init? is added [[Feature #18008]] * String * Update Unicode version to 13.0.0 [[Feature #17750]] and Emoji version to 13.0 [[Feature #18029]] * Queue * Queue#initialize now accepts an Enumerable of initial values. [[Feature #17327]] * Thread * Thread#native_thread_id is added. [[Feature #17853]] * Thread::Backtrace * Thread::Backtrace.limit, which returns the value to limit backtrace length set by `--backtrace-limit` command line option, is added. [[Feature #17479]] * $LOAD_PATH * $LOAD_PATH.resolve_feature_path does not raise. [[Feature #16043]] * Fiber Scheduler * Add support for `Addrinfo.getaddrinfo` using `address_resolve` hook. [[Feature #17370]] * Introduce non-blocking `Timeout.timeout` using `timeout_after` hook. [[Feature #17470]] * Introduce new scheduler hooks `io_read` and `io_write` along with a low level `IO::Buffer` for zero-copy read/write. [[Feature #18020]] * IO hooks `io_wait`, `io_read`, `io_write`, receive the original IO object where possible. [[Bug #18003]] * Make `Monitor` fiber-safe. [[Bug #17827]] * Replace copy coroutine with pthread implementation. [[Feature #18015]] * Refinement * New class which represents a module created by Module#refine. `include` and `prepend` are deprecated, and `import_methods` is added instead. [[Bug #17429]] ## Stdlib updates * The following default gem are updated. * RubyGems * Bundler * RDoc 6.3.2 * ReLine * JSON 2.6.1 * Psych 4.0.2 * FileUtils 1.6.0 * Fiddle 1.1.0 * StringIO 3.0.1 * IO::Console 0.5.9 * IO::Wait 0.2.1 * CSV 3.2.1 * Etc 1.3.0 * Date 3.2.2 * Zlib 2.1.1 * StringScanner 3.0.1 * IpAddr 1.2.3 * Logger 1.4.4 * OStruct 0.5.2 * Irb * Racc 1.6.0 * Delegate 0.2.0 * Benchmark 0.2.0 * CGI 0.3.1 * Readline(C-ext) 0.1.3 * Timeout 0.2.0 * YAML 0.2.0 * URI 0.11.0 * OpenSSL * DidYouMean * Weakref 0.1.1 * Tempfile 0.1.2 * TmpDir 0.1.2 * English 0.7.1 * Net::Protocol 0.1.2 * Net::Http 0.2.0 * BigDecimal * OptionParser 0.2.0 * Set 1.0.2 * Find 0.1.1 * Rinda 0.1.1 * Erb 2.2.3 * NKF 0.1.1 * Base64 0.1.1 * OpenUri 0.2.0 * SecureRandom 0.1.1 * Resolv 0.2.1 * Resolv::Replace 0.1.0 * Time 0.2.0 * PP 0.2.1 * Prettyprint 0.1.1 * Drb 2.1.0 * Pathname 0.2.0 * Digest 3.1.0.pre3 * Un 0.2.0 * The following bundled gems are updated. * minitest 5.14.4 * power_assert 2.0.1 * rake 13.0.6 * test-unit 3.5.1 * rbs 1.8.0 * typeprof 0.20.4 * The following default gems are now bundled gems. * net-ftp * net-imap * net-pop * net-smtp * matrix * prime ## Compatibility issues Excluding feature bug fixes. * `rb_io_wait_readable`, `rb_io_wait_writable` and `rb_wait_for_single_fd` are deprecated in favour of `rb_io_maybe_wait_readable`, `rb_io_maybe_wait_writable` and `rb_io_maybe_wait` respectively. `rb_thread_wait_fd` and `rb_thread_fd_writable` are deprecated. [[Bug #18003]] ## Stdlib compatibility issues * `ERB#initialize` warns `safe_level` and later arguments even without -w. [[Feature #14256]] * `lib/debug.rb` is replaced with `debug.gem` * `Kernel#pp` in `lib/pp.rb` uses the width of `IO#winsize` by default. This means that the output width is automatically changed depending on your terminal size. [[Feature #12913]] ## C API updates * Documented. [[GH-4815]] * `rb_gc_force_recycle` is deprecated and has been changed to a no-op. [[Feature #18290]] ## Implementation improvements * `instance_eval` and `instance_exec` now only allocate a singleton class when required, avoiding extra objects and improving performance. [[GH-5146]] * The performance of `Struct` accessors is improved. [[GH-5131]] * `mandatory_only?` builtin special form to improve performance on builtin methods. [[GH-5112]] ### JIT * The default `--jit-max-cache` is changed from 100 to 10000. * JIT-ed code is no longer cancelled when a TracePoint for class events is enabled. * The JIT compiler no longer skips compilation of methods longer than 1000 instructions. * `--jit-verbose` and `--jit-warning` output "JIT cancel" when JIT-ed code is disabled because TracePoint or GC.compact is used. * `RubyVM::MJIT` is renamed to `RubyVM::JIT`. [[Feature #17490]] ### YJIT: New experimental in-process JIT compiler New JIT compiler available as an experimental feature. [[Feature #18229]] See [this blog post](https://shopify.engineering/yjit-just-in-time-compiler-cruby ) introducing the project. * Disabled by default, use `--yjit` command-line option to enable YJIT. * Performance improvements on most real-world software, up to 22% on railsbench, 39% on liquid-render. * Fast warm-up times. * Limited to macOS & Linux on x86-64 platforms for now. ## Static analysis ### RBS ### TypeProf * [Experimental IDE support](https://github.com/ruby/typeprof/blob/master/doc/ide.md) has been implemented. * Many bug fixes and performance improvements since Ruby 3.0.0. ## Debugger * A new debugger [debug.gem](https://github.com/ruby/debug) is bundled. debug.gem is fast debugger implementation and it provides many features like remote debugging, colorful REPL, IDE (VSCode) integration and more. It replaces `lib/debug.rb` standard library. * `rdbg` command is also installed into `bin/` directory to start and control debugging execution. ## error_highlight A built-in gem, error_highlight, has been introduced. It includes fine-grained error location in backtrace: ``` $ ruby test.rb test.rb:1:in `
': undefined method `time' for 1:Integer (NoMethodError) 1.time {} ^^^^^ Did you mean? times ``` This gem is enabled by default. You can disable it by using a command-line option `--disable-error_highlight`. See [the repository](https://github.com/ruby/error_highlight) in detail. ## Miscellaneous changes * lib/objspace/trace.rb is added, which is a tool for tracing the object allocation. Just by requiring this file, tracing is started *immediately*. Just by `Kernel#p`, you can investigate where an object was created. Note that just requiring this file brings a large performance overhead. This is only for debugging purpose. Do not use this in production. [[Feature #17762]] * Now exceptions raised in finalizers will be printed to `STDERR`, unless `$VERBOSE` is `nil`. [[Feature #17798]] [Bug #4443]: https://bugs.ruby-lang.org/issues/4443 [Feature #6210]: https://bugs.ruby-lang.org/issues/6210 [Feature #11256]: https://bugs.ruby-lang.org/issues/11256 [Feature #11689]: https://bugs.ruby-lang.org/issues/11689 [Feature #12194]: https://bugs.ruby-lang.org/issues/12194 [Feature #12495]: https://bugs.ruby-lang.org/issues/12495 [Feature #12913]: https://bugs.ruby-lang.org/issues/12913 [Feature #14256]: https://bugs.ruby-lang.org/issues/14256 [Feature #14394]: https://bugs.ruby-lang.org/issues/14394 [Feature #14579]: https://bugs.ruby-lang.org/issues/14579 [Feature #15198]: https://bugs.ruby-lang.org/issues/15198 [Feature #15211]: https://bugs.ruby-lang.org/issues/15211 [Feature #16043]: https://bugs.ruby-lang.org/issues/16043 [Feature #16806]: https://bugs.ruby-lang.org/issues/16806 [Feature #17312]: https://bugs.ruby-lang.org/issues/17312 [Feature #17327]: https://bugs.ruby-lang.org/issues/17327 [Feature #17370]: https://bugs.ruby-lang.org/issues/17370 [Feature #17411]: https://bugs.ruby-lang.org/issues/17411 [Bug #17423]: https://bugs.ruby-lang.org/issues/17423 [Bug #17429]: https://bugs.ruby-lang.org/issues/17429 [Feature #17470]: https://bugs.ruby-lang.org/issues/17470 [Feature #17479]: https://bugs.ruby-lang.org/issues/17479 [Feature #17490]: https://bugs.ruby-lang.org/issues/17490 [Feature #17592]: https://bugs.ruby-lang.org/issues/17592 [Feature #17724]: https://bugs.ruby-lang.org/issues/17724 [Feature #17744]: https://bugs.ruby-lang.org/issues/17744 [Feature #17750]: https://bugs.ruby-lang.org/issues/17750 [Feature #17762]: https://bugs.ruby-lang.org/issues/17762 [Feature #17795]: https://bugs.ruby-lang.org/issues/17795 [Feature #17798]: https://bugs.ruby-lang.org/issues/17798 [Bug #17827]: https://bugs.ruby-lang.org/issues/17827 [Feature #17853]: https://bugs.ruby-lang.org/issues/17853 [Bug #18003]: https://bugs.ruby-lang.org/issues/18003 [Feature #18008]: https://bugs.ruby-lang.org/issues/18008 [Feature #18015]: https://bugs.ruby-lang.org/issues/18015 [Feature #18020]: https://bugs.ruby-lang.org/issues/18020 [Feature #18029]: https://bugs.ruby-lang.org/issues/18029 [Feature #18172]: https://bugs.ruby-lang.org/issues/18172 [Feature #18229]: https://bugs.ruby-lang.org/issues/18229 [Feature #18273]: https://bugs.ruby-lang.org/issues/18273 [Feature #18290]: https://bugs.ruby-lang.org/issues/18290 [GH-1509]: https://github.com/ruby/ruby/pull/1509 [GH-4815]: https://github.com/ruby/ruby/pull/4815 [GH-5112]: https://github.com/ruby/ruby/pull/5112 [GH-5131]: https://github.com/ruby/ruby/pull/5131 [GH-5146]: https://github.com/ruby/ruby/pull/5146