=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.37.9

=head1 DESCRIPTION

This document describes differences between the 5.37.8 release and the 5.37.9
release.

If you are upgrading from an earlier release such as 5.37.7, first read
L<perl5378delta>, which describes differences between 5.37.7 and 5.37.8.

=head1 Core Enhancements

=head2 New C<class> Feature

A new B<experimental> syntax is now available for defining object classes,
where per-instance data is stored in "field" variables that behave like
lexicals.

    use feature 'class';

    class Point
    {
        field $x;
        field $y;

        method zero { $x = $y = 0; }
    }

This is described in more detail in L<perlclass>.  Notes on the internals of
its implementation and other related details can be found in L<perlclassguts>.

This remains a new and experimental feature, and is very much still under
development. It will be the subject of much further addition, refinement and
alteration in future releases.  As it is experimental, it yields warnings in
the C<experimental::class> category.  These can be silenced by a
C<no warnings> statement.

    use feature 'class';
    no warnings 'experimental::class';

=head2 REG_INF has been raised from 65,536 to 2,147,483,647

Many regex quantifiers used to be limited to U16_MAX in the past, but are
now limited to I32_MAX, thus it is now possible to write /(?:word){1000000}/
for example.  Note that doing so may cause the regex engine to run longer
and use more memory.

=head2 New API functions optimize_optree and finalize_optree

There are two new API functions for operating on optree fragments, ensuring
you can invoke the required parts of the optree-generation process that might
otherwise not get invoked (e.g. when creating a custom LOGOP).  To get access
to these functions, you first need to set a C<#define> to opt-in to using
these functions.

  #define PERL_USE_VOLATILE_API

These functions are closely tied to the internals of how the interpreter
works, and could be altered or removed at any time if other internal changes
make that necessary.

=head1 Incompatible Changes

=head2 (**{ ... }) removed from the regex engine.

This feature was released as part of 5.37.8, after some use and
discussion it was seen as more problematic than understood at first
and has been removed in 5.37.9. It was only ever present in a single
development release and has never been released as part of a production perl,
thus no deprecation cycle has been performed.

=head1 Deprecations

=head2 Use of C<'> as a package name separator is deprecated

Using C<'> as package separator in a variable named in a double-quoted
string has warned since 5.28.  It is now deprecated in both string
interpolation and non-interpolated contexts, and will be removed in
Perl 5.40.

=head1 Performance Enhancements

=over 4

=item *

Temporary ("mortal") copies are no longer created during context exit for
internal static SVs that are in no danger of being prematurely freed.
[L<GH #20800|https://github.com/Perl/perl5/issues/20800>|https://github.com/Perl/perl5/issues/20800]

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<autodie> has been upgraded from version 2.34 to 2.36.

=item *

L<B> has been upgraded from version 1.87 to 1.88.

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.201 to 2.204.

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.202 to 2.204.

=item *

L<Devel::Peek> has been upgraded from version 1.32 to 1.33.

=item *

L<Devel::PPPort> has been upgraded from version 3.69 to 3.70.

=item *

L<experimental> has been upgraded from version 0.030 to 0.031.

=item *

L<feature> has been upgraded from version 1.79 to 1.80.

=item *

L<File::Find> has been upgraded from version 1.42 to 1.43.

=item *

L<IO::Compress> has been upgraded from version 2.201 to 2.204.

=item *

L<Math::Complex> has been upgraded from version 1.6 to 1.61.

=item *

L<Memoize> has been upgraded from version 1.15 to 1.16.

=item *

L<Module::CoreList> has been upgraded from version 5.20230120 to 5.20230220.

=item *

L<mro> has been upgraded from version 1.26 to 1.28.

=item *

L<Opcode> has been upgraded from version 1.63 to 1.64.

=item *

L<parent> has been upgraded from version 0.239 to 0.241.

=item *

L<Term::Cap> has been upgraded from version 1.17 to 1.18.

=item *

L<Test::Simple> has been upgraded from version 1.302191 to 1.302192.

=item *

L<Tie::File> has been upgraded from version 1.06 to 1.07.

=item *

L<UNIVERSAL> has been upgraded from version 1.14 to 1.15.

=item *

L<warnings> has been upgraded from version 1.61 to 1.62.

=back

=head1 Documentation

=head2 New Documentation

=head3 L<perlclass>

Describes the new C<class> feature.

=head3 L<perlclassguts>

Describes the internals of the new C<class> feature.

=head2 Changes to Existing Documentation

We have attempted to update the documentation to reflect the changes
listed in this document.  If you find any we have missed, open an issue
at L<https://github.com/Perl/perl5/issues>.

Additionally, the following selected changes have been made:

=head3 L<perlfunc>

=over 4

=item *

Some wording improvements have been made for the C<ucfirst>, C<push>,
C<unshift> and C<bless> functions, as well as additional examples added.

=back

=head3 L<perlvar>

=over 4

=item *

Added a section on "Scoping Rules of Regex Variables", and other wording
improvements made throughout.

=back

=head1 Diagnostics

The following additions or changes have been made to diagnostic output,
including warnings and fatal error messages.  For the complete list of
diagnostic messages, see L<perldiag>.

=head2 New Diagnostics

=head3 New Errors

=over 4

=item *

L<Attempt to bless into a class|perldiag/"Attempt to bless into a class">

(F) You are attempting to call C<bless> with a package name that is a
new-style C<class>.  This is not necessary, as instances created by the
constructor are already in the correct class.  Instances cannot be created
by other means, such as C<bless>.

=item *

L<Cannot assign :param(%s) to field %s because that name is already in use|perldiag/"Cannot assign :param(%s) to field %s because that name is already in use">

(F) An attempt was made to apply a parameter name to a field, when the name
is already being used by another field in the same class, or one of its
parent classes. This would cause a name clash so is not allowed.

=item *

L<Cannot create class %s as it already has a non-empty @ISA|perldiag/"Cannot create class %s as it already has a non-empty @ISA">

(F) An attempt was made to create a class out of a package that already has
an C<@ISA> array, and the array is not empty.  This is not permitted, as it
would lead to a class with inconsistent inheritance.

=item *

L<Cannot invoke a method of "%s" on an instance of "%s"|perldiag/"Cannot invoke a method of "%s" on
an instance of "%s"">

(F) You tried to directly call a C<method> subroutine of one class by passing
in a value that is an instance of a different class.  This is not permitted,
as the method would not have access to the correct instance fields.

=item *

L<Cannot invoke method on a non-instance|perldiag/"Cannot invoke method on a non-instance">

(F) You tried to directly call a C<method> subroutine of a class by passing
in a value that is not an instance of that class.  This is not permitted, as
the method would not then have access to its instance fields.

=item *

L<Cannot '%s' outside of a 'class'|perldiag/"Cannot '%s' outside of a 'class'">

(F) You attempted to use one of the keywords that only makes sense inside
a C<class> definition, at a location that is not inside such a class.

=item *

L<Cannot reopen existing class "%s"|perldiag/"Cannot reopen existing class "%s"">

(F) You tried to begin a C<class> definition for a class that already exists.
A class may only have one definition block.

=item *

L<Can't bless an object reference|perldiag/"Can't bless an object reference">

(F) You attempted to call C<bless> on a value that already refers to a real
object instance.

=item *

L<can't convert empty path|perldiag/"can't convert empty path">

(F) On Cygwin, you called a path conversion function with an empty path.
Only non-empty paths are legal.

=item *

L<Class already has a superclass, cannot add another|perldiag/"Class already has a superclass, cannot add another">

(F) You attempted to specify a second superclass for a C<class> by using
the C<:isa> attribute, when one is already specified.  Unlike classes
whose instances are created with C<bless>, classes created via the
C<class> keyword cannot have more than one superclass.

=item *

L<Class attribute %s requires a value|perldiag/"Class attribute %s requires a value">

(F) You specified an attribute for a class that would require a value to
be passed in parentheses, but did not provide one.  Remember that
whitespace is B<not> permitted between the attribute name and its value;
you must write this as

    class Example::Class :attr(VALUE) ...

=item *

L<Class :isa attribute requires a class but "%s" is not one|perldiag/"Class :isa attribute requires a class but "%s" is not one">

(F) When creating a subclass using the C<class> C<:isa> attribute, the
named superclass must also be a real class created using the C<class>
keyword.

=item *

L<Field already has a parameter name, cannot add another|perldiag/"Field already has a parameter name, cannot add another">

(F) A field may have at most one application of the C<:param> attribute to
assign a parameter name to it; once applied a second one is not allowed.

=item *

L<Field attribute %s requires a value|perldiag/"Field attribute %s requires a value">

(F) You specified an attribute for a field that would require a value to
be passed in parentheses, but did not provide one.  Remember that
whitespace is B<not> permitted between the attribute name and its value;
you must write this as

    field $var :attr(VALUE) ...

=item *

L<Field %s is not accessible outside a method|perldiag/"Field %s is not accessible outside a method">

(F) An attempt was made to access a field variable of a class from code
that does not appear inside the body of a C<method> subroutine.  This is not
permitted, as only methods will have access to the fields of an instance.

=item *

L<Field %s of "%s" is not accessible in a method of "%s"|perldiag/"Field %s of "%s" is not accessible in a method of "%s"">

(F) An attempt was made to access a field variable of a class, from a
method of another class nested inside the one that actually defined it.
This is not permitted, as only methods defined by a given class are
permitted to access fields of that class.

=item *

L<Only scalar fields can take a :param attribute|perldiag/"Only scalar fields can take a :param attribute">

(F) You tried to apply the C<:param> attribute to an array or hash field.
Currently this is not permitted.

=item *

L<Required parameter '%s' is missing for %s constructor|perldiag/"Required parameter '%s' is missing for %s constructor">

(F) You called the constructor for a class that has a required named
parameter, but did not pass that parameter at all.

=item *

L<Unexpected characters while parsing class :isa attribute: %s|perldiag/"Unexpected characters while parsing class :isa attribute: %s">

(F) You tried to specify something other than a single class name with an
optional trailing version number as the value for a C<class> C<:isa>
attribute.  This confused the parser.

=item *

L<Unrecognized class attribute %s|perldiag/"Unrecognized class attribute %s">

(F) You attempted to add a named attribute to a C<class> definition, but
perl does not recognise the name of the requested attribute.

=item *

L<Unrecognized field attribute %s|perldiag/"Unrecognized field attribute %s">

(F) You attempted to add a named attribute to a C<field> definition, but
perl does not recognise the name of the requested attribute.

=back

=head3 New Warnings

=over 4

=item *

L<ADJUST is experimental|perldiag/"ADJUST is experimental">

(S experimental::class) This warning is emitted if you use the C<ADJUST>
keyword of C<use feature 'class'>.  This keyword is currently
experimental and its behaviour may change in future releases of Perl.

=item *

L<class is experimental|perldiag/"class is experimental">

(S experimental::class) This warning is emitted if you use the C<class>
keyword of C<use feature 'class'>.  This keyword is currently
experimental and its behaviour may change in future releases of Perl.

=item *

L<Method %s redefined|perldiag/"Method %s redefined">

(W redefine) You redefined a method.  To suppress this warning, say

    {
       no warnings 'redefine';
       *name = method { ... };
    }

=item *

L<Odd number of elements in hash field initialization|perldiag/"Odd number of elements in hash field initialization">

(W misc) You specified an odd number of elements to initialise a hash
field of an object.  Hashes are initialised from a list of key/value
pairs so there must be a corresponding value to every key.  The final
missing value will be filled in with undef instead.

=item *

L<Old package separator "'" deprecated|perldiag/"Old package separator "'" deprecated">

(W deprecated, syntax) You used the old package separator "'" in a
variable, subroutine or package name.  Support for the old package
separator will be removed in Perl 5.40.

=item *

L<field is experimental|perldiag/"field is experimental">

(S experimental::class) This warning is emitted if you use the C<field>
keyword of C<use feature 'class'>.  This keyword is currently
experimental and its behaviour may change in future releases of Perl.

=item *

L<method is experimental|perldiag/"method is experimental">

(S experimental::class) This warning is emitted if you use the C<method>
keyword of C<use feature 'class'>.  This keyword is currently
experimental and its behaviour may change in future releases of Perl.

=back

=head2 Changes to Existing Diagnostics

=over 4

=item *

L<Old package separator used in string|perldiag/"Old package separator used in string">

This diagnostic is now also part of the C<deprecated> category.

=back

=head1 Configuration and Compilation

=over 4

=item *

C<Configure> now properly handles quoted elements outputted from gcc. [L<GH #20606|https://github.com/Perl/perl5/issues/20606>]

=item *

C<Configure> probed for the return type of malloc() and free() by
testing whether declarations for those functions produced a function
type mismatch with the implementation.  On Solaris, with a C++
compiler, this check always failed, since Solaris instead imports
malloc() and free() from C<std::> with C<using> for C++ builds.  Since
the return types of malloc() and free() are well defined by the C
standard, skip probing for them.  C<Configure> command-line arguments
and hints can still override these type in the unlikely case that is
needed.  [L<GH #20806|https://github.com/Perl/perl5/issues/20806>]

=back

=head1 Testing

Tests were added and changed to reflect the other additions and changes
in this release.

=head1 Internal Changes

=over 4

=item *

The underlying C<Perl_dowantarray> function implementing the
long-deprecated L<C<GIMME>|perlapi/GIMME> macro has been marked as
deprecated, so that use of the macro emits a compile-time warning.
C<GIMME> has been documented as deprecated in favour of
L<C<GIMME_V>|perlapi/GIMME_V> since Perl v5.6.0, but had not
previously issued a warning.

=item *

The API function L<perlapi/utf8_length> is now more efficient.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Writing to a magic variables associated with the selected output
handle, C<$^>, C<$~>, C<$=>, C<$-> and C<$%>, no longer crashes perl
if the IO object has been cleared from the selected output
handle. [L<GH #20733|https://github.com/Perl/perl5/issues/20733>]

=item *

Redefining a C<use constant> list constant with C<use constant> now
properly warns.  This changes the behaviour of C<use constant> but is
a core change, not a change to F<constant.pm>.  [L<GH #20742|https://github.com/Perl/perl5/issues/20742>]

=item *

Redefining a C<use constant> list constant with an empty prototype
constant sub would result in an assertion failure.  [L<GH #20742|https://github.com/Perl/perl5/issues/20742>]

=item *

Fixed a regression where the C<INC> method for objects in C<@INC>
would not be resolved by C<AUTOLOAD>, while it was in 5.36.  The
C<INCDIR> method for objects in C<@INC> cannot be resolved by
C<AUTOLOAD> as C<INC> would have been resolved first.  [L<GH #20665|https://github.com/Perl/perl5/issues/20665>]

=item *

C<$SIG{__DIE__}> will now be called from eval when the code dies during
compilation regardless of how it dies. This means that code expecting to
be able to upgrade C<$@> into an object will be called consistently. In
earlier versions of perl C<$SIG{__DIE__}> would not be called for
certain compilation errors, for instance undeclared variables. For other
errors it might be called if there were more than a certain number of
errors, but not if there were less. Now you can expect that it will be
called in every case.

=item *

Compilation of code with errors used to inconsistently stop depending on
the count and type of errors encountered. The intent was that after 10
errors compilation would halt, but bugs in this logic meant that certain
types of error would be counted, but would not trigger the threshold
check to stop compilation. Other errors would. With this release after
at most 10 errors compilation will terminate, regardless of what type of
error they were.

Note that you can change the maximum count by defining
C<PERL_STOP_PARSING_AFTER_N_ERRORS> to be something else during the
configuration process. For instance

    ./Configure ... -Accflags='-DPERL_STOP_PARSING_AFTER_N_ERRORS=100'

would allow up to 100 errors.

=item *

The API function L<perlapi/my_snprintf> now prints a non-dot decimal
point if the perl code it ultimately is called from is in the scope of
C<use locale> and the locale in effect calls for that.

=back

=head1 Acknowledgements

Perl 5.37.9 represents approximately 4 weeks of development since Perl
5.37.8 and contains approximately 24,000 lines of changes across 360 files
from 32 authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 8,400 lines of changes to 270 .pm, .t, .c and .h files.

Perl continues to flourish into its fourth decade thanks to a vibrant
community of users and developers. The following people are known to have
contributed the improvements that became Perl 5.37.9:

Alexander Nikolov, Alex Davies, Andrew Fresh, Aristotle Pagaltzis, Bartosz
Jarzyna, Branislav Zahradník, Chad Granum, Craig A. Berry, Dagfinn Ilmari
Mannsåker, Dan Jacobson, Elvin Aslanov, Håkon Hægland, Hugo van der
Sanden, James E Keenan, Joe McMahon, Jonathan Stowe, Karen Etheridge, Karl
Williamson, Kurt Fitzner, Leon Timmermans, Max Maischein, Nicholas Clark,
Nicolas R, Paul Evans, Paul Marquess, Renee Baecker, Richard Leach, Scott
Baker, Todd Rinaldo, Tomasz Konojacki, Tony Cook, Yves Orton.

The list above is almost certainly incomplete as it is automatically
generated from version control history. In particular, it does not include
the names of the (very much appreciated) contributors who reported issues to
the Perl bug tracker.

Many of the changes included in this version originated in the CPAN modules
included in Perl's core. We're grateful to the entire CPAN community for
helping Perl to flourish.

For a more complete list of all of Perl's historical contributors, please
see the F<AUTHORS> file in the Perl source distribution.

=head1 Reporting Bugs

If you find what you think is a bug, you might check the perl bug database
at L<https://github.com/Perl/perl5/issues>.  There may also be information at
L<http://www.perl.org/>, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at
L<https://github.com/Perl/perl5/issues>.  Be sure to trim your bug down to a
tiny but sufficient test case.

If the bug you are reporting has security implications which make it
inappropriate to send to a public issue tracker, then see
L<perlsec/SECURITY VULNERABILITY CONTACT INFORMATION>
for details of how to report the issue.

=head1 Give Thanks

If you wish to thank the Perl 5 Porters for the work we had done in Perl 5,
you can do so by running the C<perlthanks> program:

    perlthanks

This will send an email to the Perl 5 Porters list with your show of thanks.

=head1 SEE ALSO

The F<Changes> file for an explanation of how to view exhaustive details on
what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut