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# NEWS for Ruby 2.8.0 (tentative; to be 3.0.0)
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This document is a list of user visible feature changes
since the **2.7.0** release, 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`).
## Language changes
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* Keyword arguments are now separated from positional arguments.
Code that resulted in deprecation warnings in Ruby 2.7 will now
result in ArgumentError or different behavior. [[Feature #14183]]
* Procs accepting a single rest argument and keywords are no longer
subject to autosplatting. This now matches the behavior of Procs
accepting a single rest argument and no keywords.
[[Feature #16166]]
```ruby
pr = proc{|*a, **kw| [a, kw]}
pr.call([1])
# 2.7 => [[1], {}]
# 3.0 => [[[1]], {}]
pr.call([1, {a: 1}])
# 2.7 => [[1], {:a=>1}] # and deprecation warning
# 3.0 => [[[1, {:a=>1}]], {}]
```
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* $SAFE is now a normal global variable with no special behavior.
[[Feature #16131]]
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* yield in singleton class definitions in methods is now a SyntaxError
instead of a warning. yield in a class definition outside of a method
is now a SyntaxError instead of a LocalJumpError. [[Feature #15575]]
* Find pattern is added. [[Feature #16828]]
```ruby
case ["a", 1, "b", "c", 2, "d", "e", "f", 3]
in [*pre, String => x, String => y, *post]
p pre #=> ["a", 1]
p x #=> "b"
p y #=> "c"
p post #=> [2, "d", "e", "f", 3]
end
```
* Rightward assignment statement is added. [EXPERIMENTAL]
[[Feature #15921]]
```ruby
fib(10) => x
```
* Endless method definition is added. [EXPERIMENTAL]
[[Feature #16746]]
```ruby
def square(x) = x * x
```
## Command line options
### `--help` option
When the environment variable `RUBY_PAGER` or `PAGER` is present and has
non-empty value, and the standard input and output are tty, `--help`
option shows the help message via the pager designated by the value.
[[Feature #16754]]
## Core classes updates
Outstanding ones only.
* Dir
* Modified method
* Dir.glob and Dir.[] now sort the results by default, and
accept `sort:` keyword option. [[Feature #8709]]
* Hash
* Modified method
* Hash#transform_keys now accepts a hash that maps keys to new
keys. [[Feature #16274]]
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* Kernel
* Modified method
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* Kernel#clone when called with `freeze: false` keyword will call
#initialize_clone with the `freeze: false` keyword.
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[[Bug #14266]]
* Kernel#eval when called with two arguments will use "(eval)"
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for `__FILE__` and 1 for `__LINE__` in the evaluated code.
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[[Bug #4352]]
* Module
* Modified method
* Module#include now includes the arguments in modules and
classes that have already included or prepended the receiver,
mirroring the behavior if the arguments were included in the
receiver before the other modules and classes included or
prepended the receiver. [[Feature #9573]]
* Symbol
* Modified method
* Symbol#to_proc now returns a lambda Proc.
[[Feature #16260]]
## Stdlib updates
Outstanding ones only.
* RubyGems
* Update to RubyGems 3.2.0.pre1
* Bundler
* Update to Bundler 2.2.0.dev
* Net::HTTP
* New method
* Add Net::HTTP#verify_hostname= and Net::HTTP#verify_hostname
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to skip hostname verification. [[Feature #16555]]
* Modified method
* Net::HTTP.get, Net::HTTP.get_response, and Net::HTTP.get_print can
take request headers as a Hash in the second argument when the first
argument is a URI.
## Compatibility issues
Excluding feature bug fixes.
* Regexp literals are frozen [[Feature #8948]] [[Feature #16377]]
```ruby
/foo/.frozen? #=> true
```
* Bundled gems
* net-telnet and xmlrpc have been removed from the bundled gems.
If you are interested in maintaining them, please comment on
your plan to https://github.com/ruby/xmlrpc
or https://github.com/ruby/net-telnet.
* EXPERIMENTAL: Hash#each consistently yields a 2-element array [[Bug #12706]]
* Now `{ a: 1 }.each(&->(k, v) { })` raises an ArgumentError
due to lambda's arity check.
* This is experimental; if it brings a big incompatibility issue,
it may be reverted until 2.8/3.0 release.
* When writing to STDOUT redirected to a closed pipe, no broken pipe
error message will be shown now. [[Feature #14413]]
* `TRUE`/`FALSE`/`NIL` constants are no longer defined.
## Stdlib compatibility issues
Excluding feature bug fixes.
## C API updates
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* C API functions related to $SAFE have been removed.
[[Feature #16131]]
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* C API header file `ruby/ruby.h` was split. [[GH-2991]] Should have no impact
on extension libraries, but users might experience slow compilations.
## Implementation improvements
Reduce allocations for keyword argument hashes Previously, passing a keyword splat to a method always allocated a hash on the caller side, and accepting arbitrary keywords in a method allocated a separate hash on the callee side. Passing explicit keywords to a method that accepted a keyword splat did not allocate a hash on the caller side, but resulted in two hashes allocated on the callee side. This commit makes passing a single keyword splat to a method not allocate a hash on the caller side. Passing multiple keyword splats or a mix of explicit keywords and a keyword splat still generates a hash on the caller side. On the callee side, if arbitrary keywords are not accepted, it does not allocate a hash. If arbitrary keywords are accepted, it will allocate a hash, but this commit uses a callinfo flag to indicate whether the caller already allocated a hash, and if so, the callee can use the passed hash without duplicating it. So this commit should make it so that a maximum of a single hash is allocated during method calls. To set the callinfo flag appropriately, method call argument compilation checks if only a single keyword splat is given. If only one keyword splat is given, the VM_CALL_KW_SPLAT_MUT callinfo flag is not set, since in that case the keyword splat is passed directly and not mutable. If more than one splat is used, a new hash needs to be generated on the caller side, and in that case the callinfo flag is set, indicating the keyword splat is mutable by the callee. In compile_hash, used for both hash and keyword argument compilation, if compiling keyword arguments and only a single keyword splat is used, pass the argument directly. On the caller side, in vm_args.c, the callinfo flag needs to be recognized and handled. Because the keyword splat argument may not be a hash, it needs to be converted to a hash first if not. Then, unless the callinfo flag is set, the hash needs to be duplicated. The temporary copy of the callinfo flag, kw_flag, is updated if a hash was duplicated, to prevent the need to duplicate it again. If we are converting to a hash or duplicating a hash, we need to update the argument array, which can including duplicating the positional splat array if one was passed. CALLER_SETUP_ARG and a couple other places needs to be modified to handle similar issues for other types of calls. This includes fairly comprehensive tests for different ways keywords are handled internally, checking that you get equal results but that keyword splats on the caller side result in distinct objects for keyword rest parameters. Included are benchmarks for keyword argument calls. Brief results when compiled without optimization: def kw(a: 1) a end def kws(**kw) kw end h = {a: 1} kw(a: 1) # about same kw(**h) # 2.37x faster kws(a: 1) # 1.30x faster kws(**h) # 2.19x faster kw(a: 1, **h) # 1.03x slower kw(**h, **h) # about same kws(a: 1, **h) # 1.16x faster kws(**h, **h) # 1.14x faster
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* The number of hashes allocated when using a keyword splat in
a method call has been reduced to a maximum of 1, and passing
a keyword splat to a method that accepts specific keywords
does not allocate a hash.
## Miscellaneous changes
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* Methods using `ruby2_keywords` will no longer keep empty keyword
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splats, those are now removed just as they are for methods not
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using `ruby2_keywords`.
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* Taint deprecation warnings are now issued in regular mode in
addition to verbose warning mode. [[Feature #16131]]
* When an exception is caught in the default handler, the error
message and backtrace are printed in order from the innermost.
[[Feature #8661]]
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[Bug #4352]: https://bugs.ruby-lang.org/issues/4352
[Feature #8661]: https://bugs.ruby-lang.org/issues/8661
[Feature #8709]: https://bugs.ruby-lang.org/issues/8709
[Feature #8948]: https://bugs.ruby-lang.org/issues/8948
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[Feature #9573]: https://bugs.ruby-lang.org/issues/9573
[Feature #14183]: https://bugs.ruby-lang.org/issues/14183
[Bug #14266]: https://bugs.ruby-lang.org/issues/14266
[Feature #14413]: https://bugs.ruby-lang.org/issues/14413
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[Feature #15575]: https://bugs.ruby-lang.org/issues/15575
[Feature #16131]: https://bugs.ruby-lang.org/issues/16131
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[Feature #16166]: https://bugs.ruby-lang.org/issues/16166
[Feature #16260]: https://bugs.ruby-lang.org/issues/16260
[Feature #16274]: https://bugs.ruby-lang.org/issues/16274
[Feature #16377]: https://bugs.ruby-lang.org/issues/16377
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[Bug #12706]: https://bugs.ruby-lang.org/issues/12706
[Feature #15921]: https://bugs.ruby-lang.org/issues/15921
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[Feature #16555]: https://bugs.ruby-lang.org/issues/16555
[Feature #16746]: https://bugs.ruby-lang.org/issues/16746
[Feature #16754]: https://bugs.ruby-lang.org/issues/16754
[GH-2991]: https://github.com/ruby/ruby/pull/2991