ruby/NEWS

# -*- rdoc -*-

= 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. <tt>https://bugs.ruby-lang.org/issues/$FEATURE_OR_BUG_NUMBER</tt>)

== 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

    json = <<END
    {
      "name": "Alice",
      "age": 30,
      "children": [{ "name": "Bob", "age": 2 }]
    }
    END
    if JSON.parse(json, symbolize_names: true) in
         {name: "Alice", children: [{name: "Bob", age: age}]}
      p age #=> 2
    end

* See the following slides in detail
  * https://speakerdeck.com/k_tsj/pattern-matching-new-feature-in-ruby-2-dot-7

==== 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 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
      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 a keyword argument keys if 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}

* <code>**nil</code> 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)    # {}

==== Numbered parameter

* Numbered parameter as the default block parameter is introduced as an
  experimental feature.  [Feature #4475]

    [1, 2, 10].map { _1.to_s(16) } #=> ["1", "2", "a"]

==== 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 Proc.new is deprecated; use `&block` instead

* 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 not be as useful
  as an endless range, but would be good for DSL purpose.  [Feature #14799]

     ary[..3]  # identical to ary[0..3]
     where(sales: ..100)

* Setting <code>$;</code> to non-nil value is warned now.  Use of it in
  String#split is warned too.

* Setting <code>$,</code> to non-nil value is warned now.  Use of it in
  Array#join is warned too.

* Quoted here-document identifier 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 <code>self</code> as the receiver
  is now allowed. [Feature #11297] [Feature #16123]

* Modifier rescue now operates the same for multiple assignment as single
  assignment:

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

* Method reference operator, <code>.:</code> is introduced as an
  experimental feature.  [Feature #12125] [Feature #13581]

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

* Argument forwarding by <code>...</code> is introduced. [Feature #16253]

    def foo(...)
      bar(...)
    end

  All arguments to +foo+ are forwarded to +bar+, including keyword and
  block arguments.

=== Core classes updates (outstanding ones only)

Array::

  New method::

    * Added Array#intersection. [Feature #16155]

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

Complex::

  New method::

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

Dir::

  Modified method::

    * 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 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 at a name ending with a dot on
      non-Windows platforms.  [Bug #15267]

          File.extname("foo.") #=> "."

FrozenError::

  New method::

    * Added FrozenError#receiver to return the frozen object that
      modification was attempted on.  To set this object when raising
      FrozenError in Ruby code, pass it as the second argument to
      FrozenError.new.

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 friendly. [Feature #15626]

      Details on the algorithm and caveats can be found here:
      https://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 operation.  [Feature #8842]

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

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]

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 as
      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]

ObjectSpace::WeakMap::

  Modified method::

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

Regexp::

  Modified method::

    * Regexp#match and Regexp#match? with a +nil+ argument are deprecated
      and will raise a TypeError in the next release.  [Feature #13083]

RubyVM::

  Removed method::

    * +RubyVM.resolve_feature_path+ moved to
      <code>$LOAD_PATH.resolve_feature_path</code>.  [Feature #15903] [Feature #15230]

Symbol::

  Modified method::

    * Symbol#to_s now always returns a frozen String. The returned String
      is always the same for a given Symbol.  This change is
      experimental.  [Feature #16150]

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]

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 its sub
      second.  [Feature #15958]

UnboundMethod::

  New method::

    * Added UnboundMethod#bind_call method.  [Feature #15955]

      <code>umethod.bind_call(obj, ...)</code> is semantically equivalent
      to <code>umethod.bind(obj).call(...)</code>.  This idiom is used in
      some libraries to call a method that is overridden.  The added
      method does the same without allocation of 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


$LOAD_PATH::

  New method::

    * Added <code>$LOAD_PATH.resolve_feature_path</code>.  [Feature #15903] [Feature #15230]

=== Stdlib updates (outstanding ones only)

Bundler::

  * Upgrade to Bundler 2.1.0.pre.1
    Bundled from https://github.com/bundler/bundler/commit/a53709556b95a914e874b22ed2116a46b0528852

CGI::

  * CGI.escapeHTML becomes 2~5x faster when there's at least one escaped character.
    https://github.com/ruby/ruby/pull/2226

CSV::

  * Upgrade to 3.1.2.
    See https://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 highlight inspired by pry.gem to Binding#irb source lines,
    REPL input, and inspect output of some core-class objects.

  * Introduce multiline mode by Reline.

  * Show documents when completion.

  * Enable auto indent and save/load history by default.

Net::FTP::

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

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 option.  [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::

  * Delegates 3 arguments from Pathname.glob to Dir.glob to
    accept base: keyword.

Racc::

  * Merge 1.4.15 from upstream repository and added cli of racc.

Reline::

  * New stdlib that is compatible with readline stdlib by pure Ruby and also
    has a multiline mode.

REXML::

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

RSS::

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

RubyGems::

  * Upgrade to RubyGems 3.1.0.pre1
    Bundled from https://github.com/rubygems/rubygems/commit/97b264f0fa248c864b6ee9a23d3ff1cdd217dddb

StringScanner::

  * Upgrade to 1.0.3.
    See https://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)

Proc::
  * Proc#to_s format was changed. [Feature #16101]

=== Stdlib compatibility issues (excluding feature bug fixes)

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. No one maintains it from Ruby 2.0.0.

=== C API updates

* Many <code>*_kw</code> 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 <code>:</code> 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+
  https://github.com/ruby/ruby/pull/2404

=== Implementation improvements

Fiber::

  * Allow selecting different coroutine implementation 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.

File::
  * File.realpath now uses realpath(3) on many platforms, which can
    significantly improve performance.

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. ~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.

  * Default value of +--jit-max-cache+ is changed from 1,000 to 100

  * Default value of +--jit-min-calls+ is changed from 5 to 10,000

=== 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: https://bugs.ruby-lang.org/projects/ruby-trunk/wiki/C99

* Ruby's upstream repository is changed from Subversion to Git.

  * https://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.