better document version check aspect of "use"

[perl5.git] / pod / perl5275delta.pod

=encoding utf8

=head1 NAME

perl5275delta - what is new for perl v5.27.5

=head1 DESCRIPTION

This document describes differences between the 5.27.4 release and the 5.27.5
release.

If you are upgrading from an earlier release such as 5.27.3, first read
L<perl5274delta>, which describes differences between 5.27.3 and 5.27.4.

=head1 Incompatible Changes

=head2 Subroutines no longer need typeglobs

Perl 5.22.0 introduced an optimization allowing subroutines to be stored in
packages as simple sub refs, not requiring a full typeglob (thus
potentially saving large amounts of memeory).  However, the optimization
was flawed: it only applied to the main package.

This optimization has now been extended to all packages.  This may break
compatibility with introspection code that looks inside stashes and expects
everything in them to be a typeglob.

When this optimization happens, the typeglob still notionally exists, so
accessing it will cause the stash entry to be upgraded to a typeglob.  The
optimization does not apply to XSUBs or exported subroutines, and calling a
method will undo it, since method calls cache things in typeglobs.

[perl #129916] [perl #132252]

=head1 Performance Enhancements

=over 4

=item *

Calls to C<require> for an already loaded module are now slightly faster.
L<[perl #132171]|https://rt.perl.org/Public/Bug/Display.html?id=132171>

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<arybase> has been upgraded from version 0.13 to 0.14.

=item *

L<B> has been upgraded from version 1.69 to 1.70.

=item *

L<B::Concise> has been upgraded from version 1.001 to 1.002.

=item *

L<B::Deparse> has been upgraded from version 1.42 to 1.43.

=item *

L<Config::Perl::V> has been upgraded from version 0.28 to 0.29.

=item *

L<Digest::SHA> has been upgraded from version 5.96 to 5.98.

=item *

L<Encode> has been upgraded from version 2.92 to 2.93.

=item *

L<encoding> has been upgraded from version 2.20 to 2.21.

=item *

L<File::Fetch> has been upgraded from version 0.52 to 0.54.

=item *

L<File::Path> has been upgraded from version 2.14 to 2.15.

=item *

L<List::Util> has been upgraded from version 1.48 to 1.49.

=item *

L<Locale::Codes> has been upgraded from version 3.52 to 3.54.

=item *

L<Math::BigInt> has been upgraded from version 1.999806 to 1.999811.

=item *

L<Math::BigInt::FastCalc> has been upgraded from version 0.5005 to 0.5006.

=item *

L<Module::CoreList> has been upgraded from version 5.20170920 to 5.20171020.

=item *

L<NEXT> has been upgraded from version 0.67 to 0.67_01.

=item *

L<Pod::Perldoc> has been upgraded from version 3.28 to 3.2801.

=item *

L<POSIX> has been upgraded from version 1.77 to 1.78.

=item *

L<Scalar::Util> has been upgraded from version 1.48 to 1.49.

=item *

L<Sub::Util> has been upgraded from version 1.48 to 1.49.

=item *

L<Sys::Hostname> has been upgraded from version 1.20 to 1.21.

=item *

L<Test::Simple> has been upgraded from version 1.302073 to 1.302103.

=item *

L<Time::HiRes> has been upgraded from version 1.9743 to 1.9746.

=item *

L<Time::Piece> has been upgraded from version 1.3201 to 1.3202.

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item CentOS

Compilation on CentOS 5 is now fixed.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Calling L<exec PROGRAM LIST|perlfunc/exec PROGRAM LIST> with an empty C<LIST>
has been fixed.  This should call C<execvp()> with an empty C<argv> array
(containing only the terminating C<NULL> pointer), but was instead just
returning false (and not setting L<C<$!>|perlvar/$!>).
L<[perl #131730]|https://rt.perl.org/Public/Bug/Display.html?id=131730>

=item *

The C<gv_fetchmeth_sv> C function stopped working properly in Perl 5.22 when
fetching a constant with a UTF-8 name if that constant subroutine was stored in
the stash as a simple scalar reference, rather than a full typeglob.  This has
been corrected.

=item *

Single-letter debugger commands followed by an argument which starts with
punctuation  (e.g. C<p$^V> and C<x@ARGV>) now work again.  They had been
wrongly requiring a space between the command and the argument.
L<[perl #120174]|https://rt.perl.org/Public/Bug/Display.html?id=120174>

=item *

L<splice|perlfunc/splice ARRAY,OFFSET,LENGTH,LIST> now throws an exception
("Modification of a read-only value attempted") when modifying a read-only
array.  Until now it had been silently modifying the array.  The new behaviour
is consistent with the behaviour of L<push|perlfunc/push ARRAY,LIST> and
L<unshift|perlfunc/unshift ARRAY,LIST>.
L<[perl #131000]|https://rt.perl.org/Public/Bug/Display.html?id=131000>

=back

=head1 Acknowledgements

Perl 5.27.5 represents approximately 4 weeks of development since Perl 5.27.4
and contains approximately 29,000 lines of changes across 430 files from 20
authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 17,000 lines of changes to 340 .pm, .t, .c and .h files.

Perl continues to flourish into its third decade thanks to a vibrant community
of users and developers.  The following people are known to have contributed
the improvements that became Perl 5.27.5:

Aaron Crane, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari
Mannsåker, Dmitry Ulanov, Dominic Hargreaves, Father Chrysostomos, H.Merijn
Brand, James E Keenan, John P. Linderman, John SJ Anderson, Lukas Mai, Nicolas
R., Sawyer X, Smylers, Steve Hay, Tom Hukins, Tony Cook, Yves Orton, Zefram.

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://rt.perl.org/> .  There may also be information at
L<http://www.perl.org/> , the Perl Home Page.

If you believe you have an unreported bug, please run the L<perlbug> program
included with your release.  Be sure to trim your bug down to a tiny but
sufficient test case.  Your bug report, along with the output of C<perl -V>,
will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

If the bug you are reporting has security implications which make it
inappropriate to send to a publicly archived mailing list, 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