NEWS for Ruby 2.7.0

This document is a list of user visible feature changes made between releases except for bug fixes.

Note that each entry is kept so brief that no reason behind or reference information is supplied with. For a full list of changes with all sufficient information, see the ChangeLog file or Redmine (e.g. https://bugs.ruby-lang.org/issues/$FEATURE_OR_BUG_NUMBER).

Changes since the 2.6.0 release

Language changes

Pattern matching

Pattern matching is introduced as an experimental feature. [Feature #14912]

case [0, [1, 2, 3]]
in [a, [b, *c]]
  p a #=> 0
  p b #=> 1
  p c #=> [2, 3]
end

case {a: 0, b: 1}
in {a: 0, x: 1}
  :unreachable
in {a: 0, b: var}
  p var #=> 1
end

case -1
in 0 then :unreachable
in 1 then :unreachable
end #=> NoMatchingPatternError

json = <<END
{
  "name": "Alice",
  "age": 30,
  "children": [{ "name": "Bob", "age": 2 }]
}
END

JSON.parse(json, symbolize_names: true) in {name: "Alice", children: [{name: name, age: age}]}

p name #=> "Bob"
p age  #=> 2

JSON.parse(json, symbolize_names: true) in {name: "Alice", children: [{name: "Charlie", age: age}]}
#=> NoMatchingPatternError

See the following slides for more details:
- speakerdeck.com/k_tsj/pattern-matching-new-feature-in-ruby-2-dot-7
- Note that the slides are slightly obsolete.
The warning against pattern matching can be suppressed with -W:no-experimental option.

The spec of keyword arguments is changed towards 3.0

Automatic conversion of keyword arguments and positional arguments is deprecated, and conversion will be removed in Ruby 3. [Feature #14183]
- When a method call passes a Hash at the last argument, and when it passes no keywords, and when the called method accepts keywords, a warning is emitted. To continue treating the hash as keywords, add a double splat operator to avoid the warning and ensure correct behavior in Ruby 3.
```
def foo(key: 42); end; foo({key: 42})   # warned
def foo(**kw);    end; foo({key: 42})   # warned
def foo(key: 42); end; foo(**{key: 42}) # OK
def foo(**kw);    end; foo(**{key: 42}) # OK
```
- When a method call passes keywords to a method that accepts keywords, but it does not pass enough required positional arguments, the keywords are treated as a final required positional argument, and a warning is emitted. Pass the argument as a hash instead of keywords to avoid the warning and ensure correct behavior in Ruby 3.
```
def foo(h, **kw); end; foo(key: 42)      # warned
def foo(h, key: 42); end; foo(key: 42)   # warned
def foo(h, **kw); end; foo({key: 42})    # OK
def foo(h, key: 42); end; foo({key: 42}) # OK
```
- When a method accepts specific keywords but not a keyword splat, and a hash or keywords splat is passed to the method that includes both Symbol and non-Symbol keys, the hash will continue to be split, and a warning will be emitted. You will need to update the calling code to pass separate hashes to ensure correct behavior in Ruby 3.
```
def foo(h={}, key: 42); end; foo("key" => 43, key: 42)   # warned
def foo(h={}, key: 42); end; foo({"key" => 43, key: 42}) # warned
def foo(h={}, key: 42); end; foo({"key" => 43}, key: 42) # OK
```
- If a method does not accept keywords, and is called with keywords, the keywords are still treated as a positional hash, with no warning. This behavior will continue to work in Ruby 3.
```
def foo(opt={});  end; foo( key: 42 )   # OK
```
Non-symbols are allowed as keyword argument keys if the method accepts arbitrary keywords. [Feature #14183]
- Non-Symbol keys in a keyword arguments hash were prohibited in 2.6.0, but are now allowed again. [Bug #15658]
```
def foo(**kw); p kw; end; foo("str" => 1) #=> {"str"=>1}
```

**nil is allowed in method definitions to explicitly mark that the method accepts no keywords. Calling such a method with keywords will result in an ArgumentError. [Feature #14183]

def foo(h, **nil); end; foo(key: 1)       # ArgumentError
def foo(h, **nil); end; foo(**{key: 1})   # ArgumentError
def foo(h, **nil); end; foo("str" => 1)   # ArgumentError
def foo(h, **nil); end; foo({key: 1})     # OK
def foo(h, **nil); end; foo({"str" => 1}) # OK

Passing an empty keyword splat to a method that does not accept keywords no longer passes an empty hash, unless the empty hash is necessary for a required parameter, in which case a warning will be emitted. Remove the double splat to continue passing a positional hash. [Feature #14183]
```
h = {}; def foo(*a) a end; foo(**h) # []
h = {}; def foo(a) a end; foo(**h)  # {} and warning
h = {}; def foo(*a) a end; foo(h)   # [{}]
h = {}; def foo(a) a end; foo(h)    # {}
```
Above warnings can be suppressed also with -W:no-deprecated option.

Numbered parameters

Numbered parameters as default block parameters are introduced.

Feature #4475
1, 2, 10].map { _1.to_s(16) } #=> [“1”, “2”, “a”
[1, 2], [3, 4]].map { _1 + _2 } #=> [3, 7

You can still define a local variable named _1 and so on, and that is honored when present, but renders a warning.
```
_1 = 0            #=> warning: `_1' is reserved for numbered parameter; consider another name
[1].each { p _1 } # prints 0 instead of 1
```

proc/lambda without block is deprecated

Proc.new and Kernel#proc with no block in a method called with a block is warned now.
```
def foo
  proc
end
foo { puts "Hello" } #=> warning: Capturing the given block using Kernel#proc is deprecated; use `&block` instead
```
This warning can be suppressed with -W:no-deprecated option.

Kernel#lambda with no block in a method called with a block raises an exception.

def bar
  lambda
end
bar { puts "Hello" } #=> tried to create Proc object without a block (ArgumentError)

Other miscellaneous changes

A beginless range is experimentally introduced. It might be useful in case, new call-sequence of the Comparable#clamp, constants and DSLs. [Feature #14799]
```
ary[..3]  # identical to ary[0..3]

case RUBY_VERSION
when ..."2.4" then puts "EOL"
# ...
end

age.clamp(..100)

where(sales: ..100)
```
Setting $; to a non-nil value is warned now. [Feature #14240] Use of it in String#split is warned too. This warning can be suppressed with -W:no-deprecated option.
Setting $, to a non-nil value is warned now. [Feature #14240] Use of it in Array#join is warned too. This warning can be suppressed with -W:no-deprecated option.

Quoted here-document identifiers must end within the same line.

<<"EOS
" # This had been warned since 2.4; Now it raises a SyntaxError
EOS

The flip-flop syntax deprecation is reverted. [Feature #5400]
Comment lines can be placed between fluent dot now.
```
foo
  # .bar
  .baz # => foo.baz
```
Calling a private method with a literal self as the receiver is now allowed. [Feature #11297] [Feature #16123]

Modifier rescue now operates the same for multiple assignment as single assignment. [Bug #8279]

a, b = raise rescue [1, 2]
# Previously parsed as: (a, b = raise) rescue [1, 2]
# Now parsed as:         a, b = (raise rescue [1, 2])

yield in singleton class syntax is warned and will be deprecated later. [Feature #15575].

def foo
  class << Object.new
    yield #=> warning: `yield' in class syntax will not be supported from Ruby 3.0. [Feature #15575]
  end
end
foo { p :ok }

This warning can be suppressed with -W:no-deprecated option.

Argument forwarding by (...) is introduced. [Feature #16253]
```
def foo(...)
  bar(...)
end
```
All arguments to foo are forwarded to bar, including keyword and block arguments. Note that the parentheses are mandatory. bar ... is parsed as an endless range.
Access and setting of $SAFE is now always warned. $SAFE will become a normal global variable in Ruby 3.0. [Feature #16131]
Object#{taint,untaint,trust,untrust} and related functions in the C-API no longer have an effect (all objects are always considered untainted), and are now warned in verbose mode. This warning will be disabled even in non-verbose mode in Ruby 3.0, and the methods and C functions will be removed in Ruby 3.2. [Feature #16131]
Refinements take place at Object#method and Module#instance_method. [Feature #15373]

Command line options

Warning option

The -W option has been extended with a following :, to manage categorized warnings. [Feature #16345] [Feature #16420]

To suppress deprecation warnings:

$ ruby -e '$; = ""'
-e:1: warning: `$;' is deprecated

$ ruby -W:no-deprecated -e '$; = //'

It works with the RUBYOPT environment variable:
```
$ RUBYOPT=-W:no-deprecated ruby -e '$; = //'
```

To suppress experimental feature warnings:

$ ruby -e '0 in a'
-e:1: warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!

$ ruby -W:no-experimental -e '0 in a'

To suppress both by using RUBYOPT, set space separated values:

$ RUBYOPT='-W:no-deprecated -W:no-experimental' ruby -e '($; = "") in a'

See also Warning in Core classes updates.

Core classes updates (outstanding ones only)

Array

New methods

Added Array#intersection. [Feature #16155]
Added Array#minmax, with a faster implementation than Enumerable#minmax. [Bug #15929]

Comparable

Modified method

Comparable#clamp now accepts a Range argument. [Feature #14784]

-1.clamp(0..2) #=> 0
 1.clamp(0..2) #=> 1
 3.clamp(0..2) #=> 2
# With beginless and endless ranges:
-1.clamp(0..)  #=> 0
 3.clamp(..2)  #=> 2

Complex

New method

Added Complex#<=>. So 0 <=> 0i will not raise NoMethodError. [Bug #15857]

Dir

Modified methods

Dir.glob and Dir.[] no longer allow NUL-separated glob pattern. Use Array instead. [Feature #14643]

Encoding

New encoding

Added new encoding CESU-8. [Feature #15931]

Enumerable

New methods

Added Enumerable#filter_map. [Feature #15323]

[1, 2, 3].filter_map {|x| x.odd? ? x.to_s : nil } #=> ["1", "3"]

Added Enumerable#tally. [Feature #11076]

["A", "B", "C", "B", "A"].tally #=> {"A"=>2, "B"=>2, "C"=>1}

Enumerator

New methods

Added Enumerator.produce to generate an Enumerator from any custom data transformation. [Feature #14781]

require "date"
dates = Enumerator.produce(Date.today, &:succ) #=> infinite sequence of dates
dates.detect(&:tuesday?) #=> next Tuesday

Added Enumerator::Lazy#eager that generates a non-lazy enumerator from a lazy enumerator. [Feature #15901]

a = %w(foo bar baz)
e = a.lazy.map {|x| x.upcase }.map {|x| x + "!" }.eager
p e.class               #=> Enumerator
p e.map {|x| x + "?" }  #=> ["FOO!?", "BAR!?", "BAZ!?"]

Added Enumerator::Yielder#to_proc so that a Yielder object can be directly passed to another method as a block argument. [Feature #15618]

Fiber

New method

Added Fiber#raise that behaves like Fiber#resume but raises an exception on the resumed fiber. [Feature #10344]

File

Modified method

File.extname now returns a dot string for names ending with a dot on non-Windows platforms. [Bug #15267]
```
File.extname("foo.") #=> "."
```

FrozenError

New method

Added FrozenError#receiver to return the frozen object on which modification was attempted. To set this object when raising FrozenError in Ruby code, FrozenError.new accepts a :receiver option. [Feature #15751]

GC

New method

Added GC.compact method for compacting the heap. This function compacts live objects in the heap so that fewer pages may be used, and the heap may be more CoW (copy-on-write) friendly. [Feature #15626]

Details on the algorithm and caveats can be found here: bugs.ruby-lang.org/issues/15626

IO

New method

Added IO#set_encoding_by_bom to check the BOM and set the external encoding. [Bug #15210]

Integer

Modified method

Integer#[] now supports range operations. [Feature #8842]

0b01001101[2, 4]  #=> 0b0011
0b01001100[2..5]  #=> 0b0011
0b01001100[2...6] #=> 0b0011
#   ^^^^

Method

Modified method

Method#inspect shows more information. [Feature #14145]

Module

New methods

Added Module#const_source_location to retrieve the location where a constant is defined. [Feature #10771]
Added Module#ruby2_keywords for marking a method as passing keyword arguments through a regular argument splat, useful when delegating all arguments to another method in a way that can be backwards compatible with older Ruby versions. [Bug #16154]

Modified methods

Module#autoload? now takes an inherit optional argument, like Module#const_defined?. [Feature #15777]
Module#name now always returns a frozen String. The returned String is always the same for a given Module. This change is experimental. [Feature #16150]

NilClass / TrueClass / FalseClass

Modified methods

NilClass#to_s, TrueClass#to_s, and FalseClass#to_s now always return a frozen String. The returned String is always the same for each of these values. This change is experimental. [Feature #16150]

ObjectSpace::WeakMap

Modified method

ObjectSpace::WeakMap#[]= now accepts special objects as either key or values. [Feature #16035]

Proc

New method

Added Proc#ruby2_keywords for marking the proc as passing keyword arguments through a regular argument splat, useful when delegating all arguments to another method or proc in a way that can be backwards compatible with older Ruby versions. [Feature #16404]

Range

New method

Added Range#minmax, with a faster implementation than Enumerable#minmax. It returns a maximum that now corresponds to Range#max. [Bug #15807]

Modified method

Range#=== now uses Range#cover? for String arguments, too (in Ruby 2.6, it was changed from Range#include? for all types except strings). [Bug #15449]

RubyVM

Removed method

RubyVM.resolve_feature_path moved to $LOAD_PATH.resolve_feature_path. [Feature #15903] [Feature #15230]

String

Unicode

Update Unicode version and Emoji version from 11.0.0 to 12.0.0. [Feature #15321]
Update Unicode version to 12.1.0, adding support for U+32FF SQUARE ERA NAME REIWA. [Feature #15195]
Update Unicode Emoji version to 12.1. [Feature #16272]

Symbol

New methods

Added Symbol#start_with? and Symbol#end_with? methods. [Feature #16348]

Time

New methods

Added Time#ceil method. [Feature #15772]
Added Time#floor method. [Feature #15653]

Modified method

Time#inspect is separated from Time#to_s and it shows the time’s sub second. [Feature #15958]

UnboundMethod

New method

Added UnboundMethod#bind_call method. [Feature #15955]

umethod.bind_call(obj, ...) is semantically equivalent to umethod.bind(obj).call(...). This idiom is used in some libraries to call a method that is overridden. The added method does the same without allocation of an intermediate Method object.

class Foo
  def add_1(x)
    x + 1
  end
end
class Bar < Foo
  def add_1(x) # override
    x + 2
  end
end

obj = Bar.new
p obj.add_1(1) #=> 3
p Foo.instance_method(:add_1).bind(obj).call(1) #=> 2
p Foo.instance_method(:add_1).bind_call(obj, 1) #=> 2

Warning

New methods

Added Warning.[] and Warning.[]= to manage emitting/suppressing some categories of warnings. [Feature #16345] [Feature #16420]

$LOAD_PATH

New method

Added $LOAD_PATH.resolve_feature_path. [Feature #15903] [Feature #15230]

Stdlib updates (outstanding ones only)

Bundler

Upgrade to Bundler 2.1.2. See github.com/bundler/bundler/releases/tag/v2.1.2

CGI

CGI.escapeHTML becomes 2~5x faster when there is at least one escaped character. See github.com/ruby/ruby/pull/2226

CSV

Upgrade to 3.1.2. See github.com/ruby/csv/blob/master/NEWS.md.

Date

Date.jisx0301, Date#jisx0301, and Date.parse support the new Japanese era. [Feature #15742]

Delegator

Object#DelegateClass accepts a block and module_evals it in the context of the returned class, similar to Class.new and Struct.new.

ERB

Prohibit marshaling ERB instance.

IRB

Introduce syntax highlighting inspired by the Pry gem to Binding#irb source lines, REPL input, and inspect output of some core-class objects.
Introduce multiline editing mode provided by Reline.
Show documentation when completion.
Enable auto indent and save/load history by default.

JSON

Upgrade to 2.3.0.

Net::FTP

Add Net::FTP#features to check available features, and Net::FTP#option to enable/disable each of them. [Feature #15964]

Net::HTTP

Add ipaddr optional parameter to Net::HTTP#start to replace the address for the TCP/IP connection. [Feature #5180]

Net::IMAP

Add Server Name Indication (SNI) support. [Feature #15594]

open-uri

Warn open-uri’s “open” method at Kernel. Use URI.open instead. [Misc #15893]
The default charset of “text/*” media type is UTF-8 instead of ISO-8859-1. [Bug #15933]

OptionParser

Now show “Did you mean?” for unknown options. [Feature #16256]

test.rb:

require "optparse"
OptionParser.new do |opts|
  opts.on("-f", "--foo", "foo") {|v| }
  opts.on("-b", "--bar", "bar") {|v| }
  opts.on("-c", "--baz", "baz") {|v| }
end.parse!

example:

$ ruby test.rb --baa
Traceback (most recent call last):
test.rb:7:in `<main>': invalid option: --baa (OptionParser::InvalidOption)
Did you mean?  baz
               bar

Pathname

Pathname.glob now delegates 3 arguments to Dir.glob to accept base keyword. [Feature #14405]

Racc

Merge 1.4.15 from upstream repository and added cli of racc.

Reline

New stdlib that is compatible with the readline stdlib but is implemented in pure Ruby. It also provides a multiline editing mode.

REXML

Upgrade to 3.2.3. See github.com/ruby/rexml/blob/master/NEWS.md.

RSS

Upgrade to RSS 0.2.8. See github.com/ruby/rss/blob/master/NEWS.md.

RubyGems

Upgrade to RubyGems 3.1.2.

StringScanner

Upgrade to 1.0.3. See github.com/ruby/strscan/blob/master/NEWS.md.

Compatibility issues (excluding feature bug fixes)

The following libraries are no longer bundled gems. Install corresponding gems to use these features.
- CMath (cmath gem)
- Scanf (scanf gem)
- Shell (shell gem)
- Synchronizer (sync gem)
- ThreadsWait (thwait gem)
- E2MM (e2mmap gem)

Proc

The Proc#to_s format was changed. [Feature #16101]

Range

Range#minmax used to iterate on the range to determine the maximum. It now uses the same algorithm as Range#max. In rare cases (e.g. ranges of Floats or Strings), this may yield different results. [Bug #15807]

Stdlib compatibility issues (excluding feature bug fixes)

Promote stdlib to default gems
- The following default gems were published on rubygems.org
  - benchmark
  - cgi
  - delegate
  - getoptlong
  - net-pop
  - net-smtp
  - open3
  - pstore
  - readline
  - readline-ext
  - singleton
- The following default gems were only promoted at ruby-core, but not yet published on rubygems.org.
  - monitor
  - observer
  - timeout
  - tracer
  - uri
  - yaml
The did_you_mean gem has been promoted up to a default gem from a bundled gem

pathname

Kernel#Pathname when called with a Pathname argument now returns the argument instead of creating a new Pathname. This is more similar to other Kernel methods, but can break code that modifies the return value and expects the argument not to be modified.

profile.rb, Profiler__

Removed from standard library. It was unmaintained since Ruby 2.0.0.

C API updates

Many *_kw functions have been added for setting whether the final argument being passed should be treated as keywords. You may need to switch to these functions to avoid keyword argument separation warnings, and to ensure correct behavior in Ruby 3.
The : character in rb_scan_args format string is now treated as keyword arguments. Passing a positional hash instead of keyword arguments will emit a deprecation warning.
C API declarations with ANYARGS are changed not to use ANYARGS. See github.com/ruby/ruby/pull/2404

Implementation improvements

Fiber

Allow selecting different coroutine implementations by using --with-coroutine=, e.g.
```
$ ./configure --with-coroutine=ucontext
$ ./configure --with-coroutine=copy
```
Replace previous stack cache with fiber pool cache. The fiber pool allocates many stacks in a single memory region. Stack allocation becomes O(log N) and fiber creation is amortized O(1). Around 10x performance improvement was measured in micro-benchmarks. github.com/ruby/ruby/pull/2224

File

File.realpath now uses realpath(3) on many platforms, which can significantly improve performance. [Feature #15797]

Hash

Change data structure of small Hash objects. [Feature #15602]

Monitor

Monitor class is written in C-extension. [Feature #16255]

Thread

VM stack memory allocation is now combined with native thread stack, improving thread allocation performance and reducing allocation related failures. Around 10x performance improvement was measured in micro-benchmarks.

JIT

JIT-ed code is recompiled to less-optimized code when an optimization assumption is invalidated.
Method inlining is performed when a method is considered as pure. This optimization is still experimental and many methods are NOT considered as pure yet.
The default value of --jit-max-cache is changed from 1,000 to 100.
The default value of --jit-min-calls is changed from 5 to 10,000.

RubyVM

Per-call-site method cache, which has been there since around 1.9, was improved: cache hit rate raised from 89% to 94%. See github.com/ruby/ruby/pull/2583

RubyVM::InstructionSequence

RubyVM::InstructionSequence#to_binary method generates compiled binary. The binary size is reduced. [Feature #16163]

Miscellaneous changes

Support for IA64 architecture has been removed. Hardware for testing was difficult to find, native fiber code is difficult to implement, and it added non-trivial complexity to the interpreter. [Feature #15894]
Require compilers to support C99. [Misc #15347]
- Details of our dialect: bugs.ruby-lang.org/projects/ruby-trunk/wiki/C99
Ruby’s upstream repository is changed from Subversion to Git.
- git.ruby-lang.org/ruby.git
- RUBY_REVISION class is changed from Integer to String.
- RUBY_DESCRIPTION includes Git revision instead of Subversion’s one.
Support built-in methods in Ruby with the _builtin syntax. [Feature #16254]

Some methods are defined in *.rb (such as trace_point.rb). For example, it is easy to define a method which accepts keyword arguments.