577 lines
19 KiB
Perl
577 lines
19 KiB
Perl
# -*- buffer-read-only: t -*-
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# !!!!!!! DO NOT EDIT THIS FILE !!!!!!!
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# This file is built by regen/feature.pl.
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# Any changes made here will be lost!
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package feature;
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our $VERSION = '1.58';
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our %feature = (
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fc => 'feature_fc',
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isa => 'feature_isa',
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say => 'feature_say',
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state => 'feature_state',
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switch => 'feature_switch',
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bitwise => 'feature_bitwise',
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indirect => 'feature_indirect',
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evalbytes => 'feature_evalbytes',
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signatures => 'feature_signatures',
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current_sub => 'feature___SUB__',
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refaliasing => 'feature_refaliasing',
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postderef_qq => 'feature_postderef_qq',
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unicode_eval => 'feature_unieval',
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declared_refs => 'feature_myref',
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unicode_strings => 'feature_unicode',
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);
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our %feature_bundle = (
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"5.10" => [qw(indirect say state switch)],
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"5.11" => [qw(indirect say state switch unicode_strings)],
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"5.15" => [qw(current_sub evalbytes fc indirect say state switch unicode_eval unicode_strings)],
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"5.23" => [qw(current_sub evalbytes fc indirect postderef_qq say state switch unicode_eval unicode_strings)],
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"5.27" => [qw(bitwise current_sub evalbytes fc indirect postderef_qq say state switch unicode_eval unicode_strings)],
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"all" => [qw(bitwise current_sub declared_refs evalbytes fc indirect isa postderef_qq refaliasing say signatures state switch unicode_eval unicode_strings)],
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"default" => [qw(indirect)],
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);
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$feature_bundle{"5.12"} = $feature_bundle{"5.11"};
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$feature_bundle{"5.13"} = $feature_bundle{"5.11"};
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$feature_bundle{"5.14"} = $feature_bundle{"5.11"};
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$feature_bundle{"5.16"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.17"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.18"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.19"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.20"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.21"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.22"} = $feature_bundle{"5.15"};
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$feature_bundle{"5.24"} = $feature_bundle{"5.23"};
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$feature_bundle{"5.25"} = $feature_bundle{"5.23"};
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$feature_bundle{"5.26"} = $feature_bundle{"5.23"};
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$feature_bundle{"5.28"} = $feature_bundle{"5.27"};
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$feature_bundle{"5.29"} = $feature_bundle{"5.27"};
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$feature_bundle{"5.30"} = $feature_bundle{"5.27"};
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$feature_bundle{"5.31"} = $feature_bundle{"5.27"};
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$feature_bundle{"5.32"} = $feature_bundle{"5.27"};
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$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
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my %noops = (
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postderef => 1,
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lexical_subs => 1,
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);
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my %removed = (
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array_base => 1,
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);
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our $hint_shift = 26;
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our $hint_mask = 0x1c000000;
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our @hint_bundles = qw( default 5.10 5.11 5.15 5.23 5.27 );
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# This gets set (for now) in $^H as well as in %^H,
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# for runtime speed of the uc/lc/ucfirst/lcfirst functions.
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# See HINT_UNI_8_BIT in perl.h.
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our $hint_uni8bit = 0x00000800;
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# TODO:
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# - think about versioned features (use feature switch => 2)
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=head1 NAME
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feature - Perl pragma to enable new features
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=head1 SYNOPSIS
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use feature qw(say switch);
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given ($foo) {
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when (1) { say "\$foo == 1" }
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when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
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when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
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when ($_ > 100) { say "\$foo > 100" }
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default { say "None of the above" }
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}
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use feature ':5.10'; # loads all features available in perl 5.10
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use v5.10; # implicitly loads :5.10 feature bundle
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=head1 DESCRIPTION
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It is usually impossible to add new syntax to Perl without breaking
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some existing programs. This pragma provides a way to minimize that
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risk. New syntactic constructs, or new semantic meanings to older
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constructs, can be enabled by C<use feature 'foo'>, and will be parsed
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only when the appropriate feature pragma is in scope. (Nevertheless, the
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C<CORE::> prefix provides access to all Perl keywords, regardless of this
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pragma.)
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=head2 Lexical effect
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Like other pragmas (C<use strict>, for example), features have a lexical
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effect. C<use feature qw(foo)> will only make the feature "foo" available
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from that point to the end of the enclosing block.
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{
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use feature 'say';
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say "say is available here";
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}
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print "But not here.\n";
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=head2 C<no feature>
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Features can also be turned off by using C<no feature "foo">. This too
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has lexical effect.
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use feature 'say';
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say "say is available here";
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{
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no feature 'say';
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print "But not here.\n";
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}
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say "Yet it is here.";
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C<no feature> with no features specified will reset to the default group. To
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disable I<all> features (an unusual request!) use C<no feature ':all'>.
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=head1 AVAILABLE FEATURES
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=head2 The 'say' feature
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C<use feature 'say'> tells the compiler to enable the Perl 6 style
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C<say> function.
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See L<perlfunc/say> for details.
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This feature is available starting with Perl 5.10.
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=head2 The 'state' feature
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C<use feature 'state'> tells the compiler to enable C<state>
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variables.
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See L<perlsub/"Persistent Private Variables"> for details.
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This feature is available starting with Perl 5.10.
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=head2 The 'switch' feature
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B<WARNING>: Because the L<smartmatch operator|perlop/"Smartmatch Operator"> is
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experimental, Perl will warn when you use this feature, unless you have
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explicitly disabled the warning:
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no warnings "experimental::smartmatch";
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C<use feature 'switch'> tells the compiler to enable the Perl 6
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given/when construct.
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See L<perlsyn/"Switch Statements"> for details.
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This feature is available starting with Perl 5.10.
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=head2 The 'unicode_strings' feature
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C<use feature 'unicode_strings'> tells the compiler to use Unicode rules
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in all string operations executed within its scope (unless they are also
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within the scope of either C<use locale> or C<use bytes>). The same applies
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to all regular expressions compiled within the scope, even if executed outside
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it. It does not change the internal representation of strings, but only how
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they are interpreted.
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C<no feature 'unicode_strings'> tells the compiler to use the traditional
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Perl rules wherein the native character set rules is used unless it is
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clear to Perl that Unicode is desired. This can lead to some surprises
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when the behavior suddenly changes. (See
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L<perlunicode/The "Unicode Bug"> for details.) For this reason, if you are
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potentially using Unicode in your program, the
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C<use feature 'unicode_strings'> subpragma is B<strongly> recommended.
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This feature is available starting with Perl 5.12; was almost fully
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implemented in Perl 5.14; and extended in Perl 5.16 to cover C<quotemeta>;
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was extended further in Perl 5.26 to cover L<the range
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operator|perlop/Range Operators>; and was extended again in Perl 5.28 to
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cover L<special-cased whitespace splitting|perlfunc/split>.
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=head2 The 'unicode_eval' and 'evalbytes' features
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Together, these two features are intended to replace the legacy string
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C<eval> function, which behaves problematically in some instances. They are
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available starting with Perl 5.16, and are enabled by default by a
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S<C<use 5.16>> or higher declaration.
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C<unicode_eval> changes the behavior of plain string C<eval> to work more
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consistently, especially in the Unicode world. Certain (mis)behaviors
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couldn't be changed without breaking some things that had come to rely on
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them, so the feature can be enabled and disabled. Details are at
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L<perlfunc/Under the "unicode_eval" feature>.
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C<evalbytes> is like string C<eval>, but operating on a byte stream that is
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not UTF-8 encoded. Details are at L<perlfunc/evalbytes EXPR>. Without a
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S<C<use feature 'evalbytes'>> nor a S<C<use v5.16>> (or higher) declaration in
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the current scope, you can still access it by instead writing
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C<CORE::evalbytes>.
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=head2 The 'current_sub' feature
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This provides the C<__SUB__> token that returns a reference to the current
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subroutine or C<undef> outside of a subroutine.
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This feature is available starting with Perl 5.16.
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=head2 The 'array_base' feature
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This feature supported the legacy C<$[> variable. See L<perlvar/$[>.
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It was on by default but disabled under C<use v5.16> (see
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L</IMPLICIT LOADING>, below) and unavailable since perl 5.30.
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This feature is available under this name starting with Perl 5.16. In
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previous versions, it was simply on all the time, and this pragma knew
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nothing about it.
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=head2 The 'fc' feature
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C<use feature 'fc'> tells the compiler to enable the C<fc> function,
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which implements Unicode casefolding.
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See L<perlfunc/fc> for details.
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This feature is available from Perl 5.16 onwards.
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=head2 The 'lexical_subs' feature
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In Perl versions prior to 5.26, this feature enabled
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declaration of subroutines via C<my sub foo>, C<state sub foo>
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and C<our sub foo> syntax. See L<perlsub/Lexical Subroutines> for details.
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This feature is available from Perl 5.18 onwards. From Perl 5.18 to 5.24,
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it was classed as experimental, and Perl emitted a warning for its
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usage, except when explicitly disabled:
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no warnings "experimental::lexical_subs";
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As of Perl 5.26, use of this feature no longer triggers a warning, though
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the C<experimental::lexical_subs> warning category still exists (for
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compatibility with code that disables it). In addition, this syntax is
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not only no longer experimental, but it is enabled for all Perl code,
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regardless of what feature declarations are in scope.
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=head2 The 'postderef' and 'postderef_qq' features
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The 'postderef_qq' feature extends the applicability of L<postfix
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dereference syntax|perlref/Postfix Dereference Syntax> so that postfix array
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and scalar dereference are available in double-quotish interpolations. For
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example, it makes the following two statements equivalent:
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my $s = "[@{ $h->{a} }]";
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my $s = "[$h->{a}->@*]";
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This feature is available from Perl 5.20 onwards. In Perl 5.20 and 5.22, it
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was classed as experimental, and Perl emitted a warning for its
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usage, except when explicitly disabled:
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no warnings "experimental::postderef";
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As of Perl 5.24, use of this feature no longer triggers a warning, though
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the C<experimental::postderef> warning category still exists (for
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compatibility with code that disables it).
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The 'postderef' feature was used in Perl 5.20 and Perl 5.22 to enable
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postfix dereference syntax outside double-quotish interpolations. In those
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versions, using it triggered the C<experimental::postderef> warning in the
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same way as the 'postderef_qq' feature did. As of Perl 5.24, this syntax is
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not only no longer experimental, but it is enabled for all Perl code,
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regardless of what feature declarations are in scope.
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=head2 The 'signatures' feature
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B<WARNING>: This feature is still experimental and the implementation may
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change in future versions of Perl. For this reason, Perl will
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warn when you use the feature, unless you have explicitly disabled the
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warning:
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no warnings "experimental::signatures";
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This enables unpacking of subroutine arguments into lexical variables
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by syntax such as
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sub foo ($left, $right) {
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return $left + $right;
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}
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See L<perlsub/Signatures> for details.
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This feature is available from Perl 5.20 onwards.
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=head2 The 'refaliasing' feature
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B<WARNING>: This feature is still experimental and the implementation may
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change in future versions of Perl. For this reason, Perl will
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warn when you use the feature, unless you have explicitly disabled the
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warning:
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no warnings "experimental::refaliasing";
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This enables aliasing via assignment to references:
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\$a = \$b; # $a and $b now point to the same scalar
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\@a = \@b; # to the same array
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\%a = \%b;
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\&a = \&b;
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foreach \%hash (@array_of_hash_refs) {
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...
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}
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See L<perlref/Assigning to References> for details.
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This feature is available from Perl 5.22 onwards.
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=head2 The 'bitwise' feature
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This makes the four standard bitwise operators (C<& | ^ ~>) treat their
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operands consistently as numbers, and introduces four new dotted operators
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(C<&. |. ^. ~.>) that treat their operands consistently as strings. The
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same applies to the assignment variants (C<&= |= ^= &.= |.= ^.=>).
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See L<perlop/Bitwise String Operators> for details.
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This feature is available from Perl 5.22 onwards. Starting in Perl 5.28,
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C<use v5.28> will enable the feature. Before 5.28, it was still
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experimental and would emit a warning in the "experimental::bitwise"
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category.
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=head2 The 'declared_refs' feature
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B<WARNING>: This feature is still experimental and the implementation may
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change in future versions of Perl. For this reason, Perl will
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warn when you use the feature, unless you have explicitly disabled the
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warning:
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no warnings "experimental::declared_refs";
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This allows a reference to a variable to be declared with C<my>, C<state>,
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our C<our>, or localized with C<local>. It is intended mainly for use in
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conjunction with the "refaliasing" feature. See L<perlref/Declaring a
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Reference to a Variable> for examples.
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This feature is available from Perl 5.26 onwards.
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=head2 The 'isa' feature
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This allows the use of the C<isa> infix operator, which tests whether the
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scalar given by the left operand is an object of the class given by the
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right operand. See L<perlop/Class Instance Operator> for more details.
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This feature is available from Perl 5.32 onwards.
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=head2 The 'indirect' feature
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This feature allows the use of L<indirect object
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syntax|perlobj/Indirect Object Syntax> for method calls, e.g. C<new
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Foo 1, 2;>. It is enabled by default, but can be turned off to
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disallow indirect object syntax.
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This feature is available under this name from Perl 5.32 onwards. In
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previous versions, it was simply on all the time. To disallow (or
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warn on) indirect object syntax on older Perls, see the L<indirect>
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CPAN module.
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=head1 FEATURE BUNDLES
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It's possible to load multiple features together, using
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a I<feature bundle>. The name of a feature bundle is prefixed with
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a colon, to distinguish it from an actual feature.
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use feature ":5.10";
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The following feature bundles are available:
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bundle features included
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--------- -----------------
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:default indirect
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:5.10 say state switch indirect
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:5.12 say state switch unicode_strings indirect
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:5.14 say state switch unicode_strings indirect
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:5.16 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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indirect
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:5.18 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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indirect
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:5.20 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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indirect
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:5.22 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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indirect
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:5.24 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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postderef_qq indirect
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:5.26 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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postderef_qq indirect
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:5.28 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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postderef_qq bitwise indirect
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:5.30 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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postderef_qq bitwise indirect
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:5.32 say state switch unicode_strings
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unicode_eval evalbytes current_sub fc
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postderef_qq bitwise indirect
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The C<:default> bundle represents the feature set that is enabled before
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any C<use feature> or C<no feature> declaration.
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Specifying sub-versions such as the C<0> in C<5.14.0> in feature bundles has
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no effect. Feature bundles are guaranteed to be the same for all sub-versions.
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use feature ":5.14.0"; # same as ":5.14"
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use feature ":5.14.1"; # same as ":5.14"
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=head1 IMPLICIT LOADING
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Instead of loading feature bundles by name, it is easier to let Perl do
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implicit loading of a feature bundle for you.
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There are two ways to load the C<feature> pragma implicitly:
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=over 4
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=item *
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By using the C<-E> switch on the Perl command-line instead of C<-e>.
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That will enable the feature bundle for that version of Perl in the
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main compilation unit (that is, the one-liner that follows C<-E>).
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=item *
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By explicitly requiring a minimum Perl version number for your program, with
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the C<use VERSION> construct. That is,
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use v5.10.0;
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will do an implicit
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no feature ':all';
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use feature ':5.10';
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and so on. Note how the trailing sub-version
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is automatically stripped from the
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version.
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But to avoid portability warnings (see L<perlfunc/use>), you may prefer:
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use 5.010;
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with the same effect.
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If the required version is older than Perl 5.10, the ":default" feature
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bundle is automatically loaded instead.
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Unlike C<use feature ":5.12">, saying C<use v5.12> (or any higher version)
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also does the equivalent of C<use strict>; see L<perlfunc/use> for details.
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=back
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=cut
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sub import {
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shift;
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if (!@_) {
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croak("No features specified");
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}
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__common(1, @_);
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}
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sub unimport {
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shift;
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# A bare C<no feature> should reset to the default bundle
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if (!@_) {
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$^H &= ~($hint_uni8bit|$hint_mask);
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return;
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}
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__common(0, @_);
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}
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sub __common {
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my $import = shift;
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my $bundle_number = $^H & $hint_mask;
|
|
my $features = $bundle_number != $hint_mask
|
|
&& $feature_bundle{$hint_bundles[$bundle_number >> $hint_shift]};
|
|
if ($features) {
|
|
# Features are enabled implicitly via bundle hints.
|
|
# Delete any keys that may be left over from last time.
|
|
delete @^H{ values(%feature) };
|
|
$^H |= $hint_mask;
|
|
for (@$features) {
|
|
$^H{$feature{$_}} = 1;
|
|
$^H |= $hint_uni8bit if $_ eq 'unicode_strings';
|
|
}
|
|
}
|
|
while (@_) {
|
|
my $name = shift;
|
|
if (substr($name, 0, 1) eq ":") {
|
|
my $v = substr($name, 1);
|
|
if (!exists $feature_bundle{$v}) {
|
|
$v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
|
|
if (!exists $feature_bundle{$v}) {
|
|
unknown_feature_bundle(substr($name, 1));
|
|
}
|
|
}
|
|
unshift @_, @{$feature_bundle{$v}};
|
|
next;
|
|
}
|
|
if (!exists $feature{$name}) {
|
|
if (exists $noops{$name}) {
|
|
next;
|
|
}
|
|
if (!$import && exists $removed{$name}) {
|
|
next;
|
|
}
|
|
unknown_feature($name);
|
|
}
|
|
if ($import) {
|
|
$^H{$feature{$name}} = 1;
|
|
$^H |= $hint_uni8bit if $name eq 'unicode_strings';
|
|
} else {
|
|
delete $^H{$feature{$name}};
|
|
$^H &= ~ $hint_uni8bit if $name eq 'unicode_strings';
|
|
}
|
|
}
|
|
}
|
|
|
|
sub unknown_feature {
|
|
my $feature = shift;
|
|
croak(sprintf('Feature "%s" is not supported by Perl %vd',
|
|
$feature, $^V));
|
|
}
|
|
|
|
sub unknown_feature_bundle {
|
|
my $feature = shift;
|
|
croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
|
|
$feature, $^V));
|
|
}
|
|
|
|
sub croak {
|
|
require Carp;
|
|
Carp::croak(@_);
|
|
}
|
|
|
|
1;
|
|
|
|
# ex: set ro:
|