ruby--ruby/NEWS.md

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]

• Queue

  • Queue#initialize now accepts an Enumerable of initial values. [Feature #17327]

• Thread::Backtrace

  • Thread::Backtrace.limit, which returns the value to limit backtrace length set by --backtracse-limit command line option, is added. [Feature #17479]

• $LOAD_PATH

  • $LOAD_PATH.resolve_feature_path does not raise. [Feature #16043]

Stdlib updates

Outstanding ones only.

Compatibility issues

Excluding feature bug fixes.

Stdlib compatibility issues

• ERB#initialize warns safe_level and later arguments even without -w. [Feature #14256]

C API updates

Implementation improvements

JIT

• RubyVM::MJIT is renamed to RubyVM::JIT.

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