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

Pin operator now takes an expression. [Feature #17411]

Prime.each_cons(2).lazy.find_all{_1 in [n, ^(n + 2)]}.take(3).to_a
#=> [[3, 5], [5, 7], [11, 13]]

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:
```
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:
```
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]

Command line options

Core classes updates

Outstanding ones only.

Array
- Array#intersect? is added. [Feature #15198]
Enumerable
- Enumerable#compact is added. [Feature #17312]
- Enumerable#tally now accepts an optional hash to count. [Feature #17744]
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]
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]
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
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]
- 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]

Stdlib updates

Outstanding ones only.

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]

C API updates

Implementation improvements

JIT

The default --jit-max-cache is changed from 100 to 10000.
The JIT compiler no longer skips compilation of methods longer than 1000 instructions.
RubyVM::MJIT is renamed to RubyVM::JIT. [Feature #17490]

Static analysis

RBS

TypeProf

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

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