Initial Windows agent repository
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OGP64/usr/share/perl5/5.40/feature.pm
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OGP64/usr/share/perl5/5.40/feature.pm
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# -*- mode: 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.
|
||||
# Any changes made here will be lost!
|
||||
|
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package feature;
|
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our $VERSION = '1.89';
|
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|
||||
our %feature = (
|
||||
fc => 'feature_fc',
|
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isa => 'feature_isa',
|
||||
say => 'feature_say',
|
||||
try => 'feature_try',
|
||||
class => 'feature_class',
|
||||
defer => 'feature_defer',
|
||||
state => 'feature_state',
|
||||
switch => 'feature_switch',
|
||||
bitwise => 'feature_bitwise',
|
||||
indirect => 'feature_indirect',
|
||||
evalbytes => 'feature_evalbytes',
|
||||
signatures => 'feature_signatures',
|
||||
current_sub => 'feature___SUB__',
|
||||
module_true => 'feature_module_true',
|
||||
refaliasing => 'feature_refaliasing',
|
||||
postderef_qq => 'feature_postderef_qq',
|
||||
unicode_eval => 'feature_unieval',
|
||||
declared_refs => 'feature_myref',
|
||||
unicode_strings => 'feature_unicode',
|
||||
multidimensional => 'feature_multidimensional',
|
||||
bareword_filehandles => 'feature_bareword_filehandles',
|
||||
extra_paired_delimiters => 'feature_more_delims',
|
||||
);
|
||||
|
||||
our %feature_bundle = (
|
||||
"5.10" => [qw(bareword_filehandles indirect multidimensional say state switch)],
|
||||
"5.11" => [qw(bareword_filehandles indirect multidimensional say state switch unicode_strings)],
|
||||
"5.15" => [qw(bareword_filehandles current_sub evalbytes fc indirect multidimensional say state switch unicode_eval unicode_strings)],
|
||||
"5.23" => [qw(bareword_filehandles current_sub evalbytes fc indirect multidimensional postderef_qq say state switch unicode_eval unicode_strings)],
|
||||
"5.27" => [qw(bareword_filehandles bitwise current_sub evalbytes fc indirect multidimensional postderef_qq say state switch unicode_eval unicode_strings)],
|
||||
"5.35" => [qw(bareword_filehandles bitwise current_sub evalbytes fc isa postderef_qq say signatures state unicode_eval unicode_strings)],
|
||||
"5.37" => [qw(bitwise current_sub evalbytes fc isa module_true postderef_qq say signatures state unicode_eval unicode_strings)],
|
||||
"5.39" => [qw(bitwise current_sub evalbytes fc isa module_true postderef_qq say signatures state try unicode_eval unicode_strings)],
|
||||
"all" => [qw(bareword_filehandles bitwise class current_sub declared_refs defer evalbytes extra_paired_delimiters fc indirect isa module_true multidimensional postderef_qq refaliasing say signatures state switch try unicode_eval unicode_strings)],
|
||||
"default" => [qw(bareword_filehandles indirect multidimensional)],
|
||||
);
|
||||
|
||||
$feature_bundle{"5.12"} = $feature_bundle{"5.11"};
|
||||
$feature_bundle{"5.13"} = $feature_bundle{"5.11"};
|
||||
$feature_bundle{"5.14"} = $feature_bundle{"5.11"};
|
||||
$feature_bundle{"5.16"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.17"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.18"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.19"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.20"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.21"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.22"} = $feature_bundle{"5.15"};
|
||||
$feature_bundle{"5.24"} = $feature_bundle{"5.23"};
|
||||
$feature_bundle{"5.25"} = $feature_bundle{"5.23"};
|
||||
$feature_bundle{"5.26"} = $feature_bundle{"5.23"};
|
||||
$feature_bundle{"5.28"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.29"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.30"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.31"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.32"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.33"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.34"} = $feature_bundle{"5.27"};
|
||||
$feature_bundle{"5.36"} = $feature_bundle{"5.35"};
|
||||
$feature_bundle{"5.38"} = $feature_bundle{"5.37"};
|
||||
$feature_bundle{"5.40"} = $feature_bundle{"5.39"};
|
||||
$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
|
||||
my %noops = (
|
||||
postderef => 1,
|
||||
lexical_subs => 1,
|
||||
);
|
||||
my %removed = (
|
||||
array_base => 1,
|
||||
);
|
||||
|
||||
our $hint_shift = 26;
|
||||
our $hint_mask = 0x3c000000;
|
||||
our @hint_bundles = qw( default 5.10 5.11 5.15 5.23 5.27 5.35 5.37 5.39 );
|
||||
|
||||
# This gets set (for now) in $^H as well as in %^H,
|
||||
# for runtime speed of the uc/lc/ucfirst/lcfirst functions.
|
||||
# See HINT_UNI_8_BIT in perl.h.
|
||||
our $hint_uni8bit = 0x00000800;
|
||||
|
||||
# TODO:
|
||||
# - think about versioned features (use feature switch => 2)
|
||||
|
||||
=encoding utf8
|
||||
|
||||
=head1 NAME
|
||||
|
||||
feature - Perl pragma to enable new features
|
||||
|
||||
=head1 SYNOPSIS
|
||||
|
||||
use feature qw(fc say);
|
||||
|
||||
# Without the "use feature" above, this code would not be able to find
|
||||
# the built-ins "say" or "fc":
|
||||
say "The case-folded version of $x is: " . fc $x;
|
||||
|
||||
|
||||
# set features to match the :5.36 bundle, which may turn off or on
|
||||
# multiple features (see "FEATURE BUNDLES" below)
|
||||
use feature ':5.36';
|
||||
|
||||
|
||||
# implicitly loads :5.36 feature bundle
|
||||
use v5.36;
|
||||
|
||||
=head1 DESCRIPTION
|
||||
|
||||
It is usually impossible to add new syntax to Perl without breaking
|
||||
some existing programs. This pragma provides a way to minimize that
|
||||
risk. New syntactic constructs, or new semantic meanings to older
|
||||
constructs, can be enabled by C<use feature 'foo'>, and will be parsed
|
||||
only when the appropriate feature pragma is in scope. (Nevertheless, the
|
||||
C<CORE::> prefix provides access to all Perl keywords, regardless of this
|
||||
pragma.)
|
||||
|
||||
=head2 Lexical effect
|
||||
|
||||
Like other pragmas (C<use strict>, for example), features have a lexical
|
||||
effect. C<use feature qw(foo)> will only make the feature "foo" available
|
||||
from that point to the end of the enclosing block.
|
||||
|
||||
{
|
||||
use feature 'say';
|
||||
say "say is available here";
|
||||
}
|
||||
print "But not here.\n";
|
||||
|
||||
=head2 C<no feature>
|
||||
|
||||
Features can also be turned off by using C<no feature "foo">. This too
|
||||
has lexical effect.
|
||||
|
||||
use feature 'say';
|
||||
say "say is available here";
|
||||
{
|
||||
no feature 'say';
|
||||
print "But not here.\n";
|
||||
}
|
||||
say "Yet it is here.";
|
||||
|
||||
C<no feature> with no features specified will reset to the default group. To
|
||||
disable I<all> features (an unusual request!) use C<no feature ':all'>.
|
||||
|
||||
=head1 AVAILABLE FEATURES
|
||||
|
||||
Read L</"FEATURE BUNDLES"> for the feature cheat sheet summary.
|
||||
|
||||
=head2 The 'say' feature
|
||||
|
||||
C<use feature 'say'> tells the compiler to enable the Raku-inspired
|
||||
C<say> function.
|
||||
|
||||
See L<perlfunc/say> for details.
|
||||
|
||||
This feature is available starting with Perl 5.10.
|
||||
|
||||
=head2 The 'state' feature
|
||||
|
||||
C<use feature 'state'> tells the compiler to enable C<state>
|
||||
variables.
|
||||
|
||||
See L<perlsub/"Persistent Private Variables"> for details.
|
||||
|
||||
This feature is available starting with Perl 5.10.
|
||||
|
||||
=head2 The 'switch' feature
|
||||
|
||||
B<WARNING>: This feature is still experimental and the implementation may
|
||||
change or be removed in future versions of Perl. For this reason, Perl will
|
||||
warn when you use the feature, unless you have explicitly disabled the warning:
|
||||
|
||||
no warnings "experimental::smartmatch";
|
||||
|
||||
C<use feature 'switch'> tells the compiler to enable the Raku
|
||||
given/when construct.
|
||||
|
||||
See L<perlsyn/"Switch Statements"> for details.
|
||||
|
||||
This feature is available starting with Perl 5.10.
|
||||
It is deprecated starting with Perl 5.38, and using
|
||||
C<given>, C<when> or smartmatch will throw a warning.
|
||||
It will be removed in Perl 5.42.
|
||||
|
||||
=head2 The 'unicode_strings' feature
|
||||
|
||||
C<use feature 'unicode_strings'> tells the compiler to use Unicode rules
|
||||
in all string operations executed within its scope (unless they are also
|
||||
within the scope of either C<use locale> or C<use bytes>). The same applies
|
||||
to all regular expressions compiled within the scope, even if executed outside
|
||||
it. It does not change the internal representation of strings, but only how
|
||||
they are interpreted.
|
||||
|
||||
C<no feature 'unicode_strings'> tells the compiler to use the traditional
|
||||
Perl rules wherein the native character set rules is used unless it is
|
||||
clear to Perl that Unicode is desired. This can lead to some surprises
|
||||
when the behavior suddenly changes. (See
|
||||
L<perlunicode/The "Unicode Bug"> for details.) For this reason, if you are
|
||||
potentially using Unicode in your program, the
|
||||
C<use feature 'unicode_strings'> subpragma is B<strongly> recommended.
|
||||
|
||||
This feature is available starting with Perl 5.12; was almost fully
|
||||
implemented in Perl 5.14; and extended in Perl 5.16 to cover C<quotemeta>;
|
||||
was extended further in Perl 5.26 to cover L<the range
|
||||
operator|perlop/Range Operators>; and was extended again in Perl 5.28 to
|
||||
cover L<special-cased whitespace splitting|perlfunc/split>.
|
||||
|
||||
=head2 The 'unicode_eval' and 'evalbytes' features
|
||||
|
||||
Together, these two features are intended to replace the legacy string
|
||||
C<eval> function, which behaves problematically in some instances. They are
|
||||
available starting with Perl 5.16, and are enabled by default by a
|
||||
S<C<use 5.16>> or higher declaration.
|
||||
|
||||
C<unicode_eval> changes the behavior of plain string C<eval> to work more
|
||||
consistently, especially in the Unicode world. Certain (mis)behaviors
|
||||
couldn't be changed without breaking some things that had come to rely on
|
||||
them, so the feature can be enabled and disabled. Details are at
|
||||
L<perlfunc/Under the "unicode_eval" feature>.
|
||||
|
||||
C<evalbytes> is like string C<eval>, but it treats its argument as a byte
|
||||
string. Details are at L<perlfunc/evalbytes EXPR>. Without a
|
||||
S<C<use feature 'evalbytes'>> nor a S<C<use v5.16>> (or higher) declaration in
|
||||
the current scope, you can still access it by instead writing
|
||||
C<CORE::evalbytes>.
|
||||
|
||||
=head2 The 'current_sub' feature
|
||||
|
||||
This provides the C<__SUB__> token that returns a reference to the current
|
||||
subroutine or C<undef> outside of a subroutine.
|
||||
|
||||
This feature is available starting with Perl 5.16.
|
||||
|
||||
=head2 The 'array_base' feature
|
||||
|
||||
This feature supported the legacy C<$[> variable. See L<perlvar/$[>.
|
||||
It was on by default but disabled under C<use v5.16> (see
|
||||
L</IMPLICIT LOADING>, below) and unavailable since perl 5.30.
|
||||
|
||||
This feature is available under this name starting with Perl 5.16. In
|
||||
previous versions, it was simply on all the time, and this pragma knew
|
||||
nothing about it.
|
||||
|
||||
=head2 The 'fc' feature
|
||||
|
||||
C<use feature 'fc'> tells the compiler to enable the C<fc> function,
|
||||
which implements Unicode casefolding.
|
||||
|
||||
See L<perlfunc/fc> for details.
|
||||
|
||||
This feature is available from Perl 5.16 onwards.
|
||||
|
||||
=head2 The 'lexical_subs' feature
|
||||
|
||||
In Perl versions prior to 5.26, this feature enabled
|
||||
declaration of subroutines via C<my sub foo>, C<state sub foo>
|
||||
and C<our sub foo> syntax. See L<perlsub/Lexical Subroutines> for details.
|
||||
|
||||
This feature is available from Perl 5.18 onwards. From Perl 5.18 to 5.24,
|
||||
it was classed as experimental, and Perl emitted a warning for its
|
||||
usage, except when explicitly disabled:
|
||||
|
||||
no warnings "experimental::lexical_subs";
|
||||
|
||||
As of Perl 5.26, use of this feature no longer triggers a warning, though
|
||||
the C<experimental::lexical_subs> warning category still exists (for
|
||||
compatibility with code that disables it). In addition, this syntax is
|
||||
not only no longer experimental, but it is enabled for all Perl code,
|
||||
regardless of what feature declarations are in scope.
|
||||
|
||||
=head2 The 'postderef' and 'postderef_qq' features
|
||||
|
||||
The 'postderef_qq' feature extends the applicability of L<postfix
|
||||
dereference syntax|perlref/Postfix Dereference Syntax> so that
|
||||
postfix array dereference, postfix scalar dereference, and
|
||||
postfix array highest index access are available in double-quotish interpolations.
|
||||
For example, it makes the following two statements equivalent:
|
||||
|
||||
my $s = "[@{ $h->{a} }]";
|
||||
my $s = "[$h->{a}->@*]";
|
||||
|
||||
This feature is available from Perl 5.20 onwards. In Perl 5.20 and 5.22, it
|
||||
was classed as experimental, and Perl emitted a warning for its
|
||||
usage, except when explicitly disabled:
|
||||
|
||||
no warnings "experimental::postderef";
|
||||
|
||||
As of Perl 5.24, use of this feature no longer triggers a warning, though
|
||||
the C<experimental::postderef> warning category still exists (for
|
||||
compatibility with code that disables it).
|
||||
|
||||
The 'postderef' feature was used in Perl 5.20 and Perl 5.22 to enable
|
||||
postfix dereference syntax outside double-quotish interpolations. In those
|
||||
versions, using it triggered the C<experimental::postderef> warning in the
|
||||
same way as the 'postderef_qq' feature did. As of Perl 5.24, this syntax is
|
||||
not only no longer experimental, but it is enabled for all Perl code,
|
||||
regardless of what feature declarations are in scope.
|
||||
|
||||
=head2 The 'signatures' feature
|
||||
|
||||
This enables syntax for declaring subroutine arguments as lexical variables.
|
||||
For example, for this subroutine:
|
||||
|
||||
sub foo ($left, $right) {
|
||||
return $left + $right;
|
||||
}
|
||||
|
||||
Calling C<foo(3, 7)> will assign C<3> into C<$left> and C<7> into C<$right>.
|
||||
|
||||
See L<perlsub/Signatures> for details.
|
||||
|
||||
This feature is available from Perl 5.20 onwards. From Perl 5.20 to 5.34,
|
||||
it was classed as experimental, and Perl emitted a warning for its usage,
|
||||
except when explicitly disabled:
|
||||
|
||||
no warnings "experimental::signatures";
|
||||
|
||||
As of Perl 5.36, use of this feature no longer triggers a warning, though the
|
||||
C<experimental::signatures> warning category still exists (for compatibility
|
||||
with code that disables it). This feature is now considered stable, and is
|
||||
enabled automatically by C<use v5.36> (or higher).
|
||||
|
||||
=head2 The 'refaliasing' feature
|
||||
|
||||
B<WARNING>: This feature is still experimental and the implementation may
|
||||
change or be removed in future versions of Perl. For this reason, Perl will
|
||||
warn when you use the feature, unless you have explicitly disabled the warning:
|
||||
|
||||
no warnings "experimental::refaliasing";
|
||||
|
||||
This enables aliasing via assignment to references:
|
||||
|
||||
\$a = \$b; # $a and $b now point to the same scalar
|
||||
\@a = \@b; # to the same array
|
||||
\%a = \%b;
|
||||
\&a = \&b;
|
||||
foreach \%hash (@array_of_hash_refs) {
|
||||
...
|
||||
}
|
||||
|
||||
See L<perlref/Assigning to References> for details.
|
||||
|
||||
This feature is available from Perl 5.22 onwards.
|
||||
|
||||
=head2 The 'bitwise' feature
|
||||
|
||||
This makes the four standard bitwise operators (C<& | ^ ~>) treat their
|
||||
operands consistently as numbers, and introduces four new dotted operators
|
||||
(C<&. |. ^. ~.>) that treat their operands consistently as strings. The
|
||||
same applies to the assignment variants (C<&= |= ^= &.= |.= ^.=>).
|
||||
|
||||
See L<perlop/Bitwise String Operators> for details.
|
||||
|
||||
This feature is available from Perl 5.22 onwards. Starting in Perl 5.28,
|
||||
C<use v5.28> will enable the feature. Before 5.28, it was still
|
||||
experimental and would emit a warning in the "experimental::bitwise"
|
||||
category.
|
||||
|
||||
=head2 The 'declared_refs' feature
|
||||
|
||||
B<WARNING>: This feature is still experimental and the implementation may
|
||||
change or be removed in future versions of Perl. For this reason, Perl will
|
||||
warn when you use the feature, unless you have explicitly disabled the warning:
|
||||
|
||||
no warnings "experimental::declared_refs";
|
||||
|
||||
This allows a reference to a variable to be declared with C<my>, C<state>,
|
||||
or C<our>, or localized with C<local>. It is intended mainly for use in
|
||||
conjunction with the "refaliasing" feature. See L<perlref/Declaring a
|
||||
Reference to a Variable> for examples.
|
||||
|
||||
This feature is available from Perl 5.26 onwards.
|
||||
|
||||
=head2 The 'isa' feature
|
||||
|
||||
This allows the use of the C<isa> infix operator, which tests whether the
|
||||
scalar given by the left operand is an object of the class given by the
|
||||
right operand. See L<perlop/Class Instance Operator> for more details.
|
||||
|
||||
This feature is available from Perl 5.32 onwards. From Perl 5.32 to 5.34,
|
||||
it was classed as experimental, and Perl emitted a warning for its usage,
|
||||
except when explicitly disabled:
|
||||
|
||||
no warnings "experimental::isa";
|
||||
|
||||
As of Perl 5.36, use of this feature no longer triggers a warning (though the
|
||||
C<experimental::isa> warning category still exists for compatibility with
|
||||
code that disables it). This feature is now considered stable, and is enabled
|
||||
automatically by C<use v5.36> (or higher).
|
||||
|
||||
=head2 The 'indirect' feature
|
||||
|
||||
This feature allows the use of L<indirect object
|
||||
syntax|perlobj/Indirect Object Syntax> for method calls, e.g. C<new
|
||||
Foo 1, 2;>. It is enabled by default, but can be turned off to
|
||||
disallow indirect object syntax.
|
||||
|
||||
This feature is available under this name from Perl 5.32 onwards. In
|
||||
previous versions, it was simply on all the time. To disallow (or
|
||||
warn on) indirect object syntax on older Perls, see the L<indirect>
|
||||
CPAN module.
|
||||
|
||||
=head2 The 'multidimensional' feature
|
||||
|
||||
This feature enables multidimensional array emulation, a perl 4 (or
|
||||
earlier) feature that was used to emulate multidimensional arrays with
|
||||
hashes. This works by converting code like C<< $foo{$x, $y} >> into
|
||||
C<< $foo{join($;, $x, $y)} >>. It is enabled by default, but can be
|
||||
turned off to disable multidimensional array emulation.
|
||||
|
||||
When this feature is disabled the syntax that is normally replaced
|
||||
will report a compilation error.
|
||||
|
||||
This feature is available under this name from Perl 5.34 onwards. In
|
||||
previous versions, it was simply on all the time.
|
||||
|
||||
You can use the L<multidimensional> module on CPAN to disable
|
||||
multidimensional array emulation for older versions of Perl.
|
||||
|
||||
=head2 The 'bareword_filehandles' feature
|
||||
|
||||
This feature enables bareword filehandles for builtin functions
|
||||
operations, a generally discouraged practice. It is enabled by
|
||||
default, but can be turned off to disable bareword filehandles, except
|
||||
for the exceptions listed below.
|
||||
|
||||
The perl built-in filehandles C<STDIN>, C<STDOUT>, C<STDERR>, C<DATA>,
|
||||
C<ARGV>, C<ARGVOUT> and the special C<_> are always enabled.
|
||||
|
||||
This feature is available under this name from Perl 5.34 onwards. In
|
||||
previous versions it was simply on all the time.
|
||||
|
||||
You can use the L<bareword::filehandles> module on CPAN to disable
|
||||
bareword filehandles for older versions of perl.
|
||||
|
||||
=head2 The 'try' feature
|
||||
|
||||
B<WARNING>: This feature is still partly experimental, and the implementation
|
||||
may change or be removed in future versions of Perl.
|
||||
|
||||
This feature enables the C<try> and C<catch> syntax, which allows exception
|
||||
handling, where exceptions thrown from the body of the block introduced with
|
||||
C<try> are caught by executing the body of the C<catch> block.
|
||||
|
||||
This feature is available starting in Perl 5.34. Before Perl 5.40 it was
|
||||
classed as experimental, and Perl emitted a warning for its usage, except when
|
||||
explicitly disabled:
|
||||
|
||||
no warnings "experimental::try";
|
||||
|
||||
As of Perl 5.40, use of this feature without a C<finally> block no longer
|
||||
triggers a warning. The optional C<finally> block is still considered
|
||||
experimental and emits a warning, except when explicitly disabled as above.
|
||||
|
||||
For more information, see L<perlsyn/"Try Catch Exception Handling">.
|
||||
|
||||
=head2 The 'defer' feature
|
||||
|
||||
B<WARNING>: This feature is still experimental and the implementation may
|
||||
change or be removed in future versions of Perl. For this reason, Perl will
|
||||
warn when you use the feature, unless you have explicitly disabled the warning:
|
||||
|
||||
no warnings "experimental::defer";
|
||||
|
||||
This feature enables the C<defer> block syntax, which allows a block of code
|
||||
to be deferred until when the flow of control leaves the block which contained
|
||||
it. For more details, see L<perlsyn/defer>.
|
||||
|
||||
This feature is available starting in Perl 5.36.
|
||||
|
||||
=head2 The 'extra_paired_delimiters' feature
|
||||
|
||||
B<WARNING>: This feature is still experimental and the implementation may
|
||||
change or be removed in future versions of Perl. For this reason, Perl will
|
||||
warn when you use the feature, unless you have explicitly disabled the warning:
|
||||
|
||||
no warnings "experimental::extra_paired_delimiters";
|
||||
|
||||
This feature enables the use of more paired string delimiters than the
|
||||
traditional four, S<C<< < > >>>, S<C<( )>>, S<C<{ }>>, and S<C<[ ]>>. When
|
||||
this feature is on, for example, you can say S<C<qrE<171>patE<187>>>.
|
||||
|
||||
As with any usage of non-ASCII delimiters in a UTF-8-encoded source file, you
|
||||
will want to ensure the parser will decode the source code from UTF-8 bytes
|
||||
with a declaration such as C<use utf8>.
|
||||
|
||||
This feature is available starting in Perl 5.36.
|
||||
|
||||
For a full list of the available characters, see
|
||||
L<perlop/List of Extra Paired Delimiters>.
|
||||
|
||||
=head2 The 'module_true' feature
|
||||
|
||||
This feature removes the need to return a true value at the end of a module
|
||||
loaded with C<require> or C<use>. Any errors during compilation will cause
|
||||
failures, but reaching the end of the module when this feature is in effect
|
||||
will prevent C<perl> from throwing an exception that the module "did not return
|
||||
a true value".
|
||||
|
||||
=head2 The 'class' feature
|
||||
|
||||
B<WARNING>: This feature is still experimental and the implementation may
|
||||
change or be removed in future versions of Perl. For this reason, Perl will
|
||||
warn when you use the feature, unless you have explicitly disabled the warning:
|
||||
|
||||
no warnings "experimental::class";
|
||||
|
||||
This feature enables the C<class> block syntax and other associated keywords
|
||||
which implement the "new" object system, previously codenamed "Corinna".
|
||||
|
||||
=head1 FEATURE BUNDLES
|
||||
|
||||
It's possible to load multiple features together, using
|
||||
a I<feature bundle>. The name of a feature bundle is prefixed with
|
||||
a colon, to distinguish it from an actual feature.
|
||||
|
||||
use feature ":5.10";
|
||||
|
||||
The following feature bundles are available:
|
||||
|
||||
bundle features included
|
||||
--------- -----------------
|
||||
:default indirect multidimensional
|
||||
bareword_filehandles
|
||||
|
||||
:5.10 bareword_filehandles indirect
|
||||
multidimensional say state switch
|
||||
|
||||
:5.12 bareword_filehandles indirect
|
||||
multidimensional say state switch
|
||||
unicode_strings
|
||||
|
||||
:5.14 bareword_filehandles indirect
|
||||
multidimensional say state switch
|
||||
unicode_strings
|
||||
|
||||
:5.16 bareword_filehandles current_sub evalbytes
|
||||
fc indirect multidimensional say state
|
||||
switch unicode_eval unicode_strings
|
||||
|
||||
:5.18 bareword_filehandles current_sub evalbytes
|
||||
fc indirect multidimensional say state
|
||||
switch unicode_eval unicode_strings
|
||||
|
||||
:5.20 bareword_filehandles current_sub evalbytes
|
||||
fc indirect multidimensional say state
|
||||
switch unicode_eval unicode_strings
|
||||
|
||||
:5.22 bareword_filehandles current_sub evalbytes
|
||||
fc indirect multidimensional say state
|
||||
switch unicode_eval unicode_strings
|
||||
|
||||
:5.24 bareword_filehandles current_sub evalbytes
|
||||
fc indirect multidimensional postderef_qq
|
||||
say state switch unicode_eval
|
||||
unicode_strings
|
||||
|
||||
:5.26 bareword_filehandles current_sub evalbytes
|
||||
fc indirect multidimensional postderef_qq
|
||||
say state switch unicode_eval
|
||||
unicode_strings
|
||||
|
||||
:5.28 bareword_filehandles bitwise current_sub
|
||||
evalbytes fc indirect multidimensional
|
||||
postderef_qq say state switch unicode_eval
|
||||
unicode_strings
|
||||
|
||||
:5.30 bareword_filehandles bitwise current_sub
|
||||
evalbytes fc indirect multidimensional
|
||||
postderef_qq say state switch unicode_eval
|
||||
unicode_strings
|
||||
|
||||
:5.32 bareword_filehandles bitwise current_sub
|
||||
evalbytes fc indirect multidimensional
|
||||
postderef_qq say state switch unicode_eval
|
||||
unicode_strings
|
||||
|
||||
:5.34 bareword_filehandles bitwise current_sub
|
||||
evalbytes fc indirect multidimensional
|
||||
postderef_qq say state switch unicode_eval
|
||||
unicode_strings
|
||||
|
||||
:5.36 bareword_filehandles bitwise current_sub
|
||||
evalbytes fc isa postderef_qq say signatures
|
||||
state unicode_eval unicode_strings
|
||||
|
||||
:5.38 bitwise current_sub evalbytes fc isa
|
||||
module_true postderef_qq say signatures
|
||||
state unicode_eval unicode_strings
|
||||
|
||||
:5.40 bitwise current_sub evalbytes fc isa
|
||||
module_true postderef_qq say signatures
|
||||
state try unicode_eval unicode_strings
|
||||
|
||||
The C<:default> bundle represents the feature set that is enabled before
|
||||
any C<use feature> or C<no feature> declaration.
|
||||
|
||||
Specifying sub-versions such as the C<0> in C<5.14.0> in feature bundles has
|
||||
no effect. Feature bundles are guaranteed to be the same for all sub-versions.
|
||||
|
||||
use feature ":5.14.0"; # same as ":5.14"
|
||||
use feature ":5.14.1"; # same as ":5.14"
|
||||
|
||||
You can also do:
|
||||
|
||||
use feature ":all";
|
||||
|
||||
or
|
||||
|
||||
no feature ":all";
|
||||
|
||||
but the first may enable features in a later version of Perl that
|
||||
change the meaning of your code, and the second may disable mechanisms
|
||||
that are part of Perl's current behavior that have been turned into
|
||||
features, just as C<indirect> and C<bareword_filehandles> were.
|
||||
|
||||
=head1 IMPLICIT LOADING
|
||||
|
||||
Instead of loading feature bundles by name, it is easier to let Perl do
|
||||
implicit loading of a feature bundle for you.
|
||||
|
||||
There are two ways to load the C<feature> pragma implicitly:
|
||||
|
||||
=over 4
|
||||
|
||||
=item *
|
||||
|
||||
By using the C<-E> switch on the Perl command-line instead of C<-e>.
|
||||
That will enable the feature bundle for that version of Perl in the
|
||||
main compilation unit (that is, the one-liner that follows C<-E>).
|
||||
|
||||
=item *
|
||||
|
||||
By explicitly requiring a minimum Perl version number for your program, with
|
||||
the C<use VERSION> construct. That is,
|
||||
|
||||
use v5.36.0;
|
||||
|
||||
will do an implicit
|
||||
|
||||
no feature ':all';
|
||||
use feature ':5.36';
|
||||
|
||||
and so on. Note how the trailing sub-version
|
||||
is automatically stripped from the
|
||||
version.
|
||||
|
||||
But to avoid portability warnings (see L<perlfunc/use>), you may prefer:
|
||||
|
||||
use 5.036;
|
||||
|
||||
with the same effect.
|
||||
|
||||
If the required version is older than Perl 5.10, the ":default" feature
|
||||
bundle is automatically loaded instead.
|
||||
|
||||
Unlike C<use feature ":5.12">, saying C<use v5.12> (or any higher version)
|
||||
also does the equivalent of C<use strict>; see L<perlfunc/use> for details.
|
||||
|
||||
=back
|
||||
|
||||
=head1 CHECKING FEATURES
|
||||
|
||||
C<feature> provides some simple APIs to check which features are enabled.
|
||||
|
||||
These functions cannot be imported and must be called by their fully
|
||||
qualified names. If you don't otherwise need to set a feature you will
|
||||
need to ensure C<feature> is loaded with:
|
||||
|
||||
use feature ();
|
||||
|
||||
=over
|
||||
|
||||
=item feature_enabled($feature)
|
||||
|
||||
=item feature_enabled($feature, $depth)
|
||||
|
||||
package MyStandardEnforcer;
|
||||
use feature ();
|
||||
use Carp "croak";
|
||||
sub import {
|
||||
croak "disable indirect!" if feature::feature_enabled("indirect");
|
||||
}
|
||||
|
||||
Test whether a named feature is enabled at a given level in the call
|
||||
stack, returning a true value if it is. C<$depth> defaults to 1,
|
||||
which checks the scope that called the scope calling
|
||||
feature::feature_enabled().
|
||||
|
||||
croaks for an unknown feature name.
|
||||
|
||||
=item features_enabled()
|
||||
|
||||
=item features_enabled($depth)
|
||||
|
||||
package ReportEnabledFeatures;
|
||||
use feature "say";
|
||||
sub import {
|
||||
say STDERR join " ", feature::features_enabled();
|
||||
}
|
||||
|
||||
Returns a list of the features enabled at a given level in the call
|
||||
stack. C<$depth> defaults to 1, which checks the scope that called
|
||||
the scope calling feature::features_enabled().
|
||||
|
||||
=item feature_bundle()
|
||||
|
||||
=item feature_bundle($depth)
|
||||
|
||||
Returns the feature bundle, if any, selected at a given level in the
|
||||
call stack. C<$depth> defaults to 1, which checks the scope that called
|
||||
the scope calling feature::feature_bundle().
|
||||
|
||||
Returns an undefined value if no feature bundle is selected in the
|
||||
scope.
|
||||
|
||||
The bundle name returned will be for the earliest bundle matching the
|
||||
selected bundle, so:
|
||||
|
||||
use feature ();
|
||||
use v5.12;
|
||||
BEGIN { print feature::feature_bundle(0); }
|
||||
|
||||
will print C<5.11>.
|
||||
|
||||
This returns internal state, at this point C<use v5.12;> sets the
|
||||
feature bundle, but C< use feature ":5.12"; > does not set the feature
|
||||
bundle. This may change in a future release of perl.
|
||||
|
||||
=back
|
||||
|
||||
=cut
|
||||
|
||||
sub import {
|
||||
shift;
|
||||
|
||||
if (!@_) {
|
||||
croak("No features specified");
|
||||
}
|
||||
|
||||
__common(1, @_);
|
||||
}
|
||||
|
||||
sub unimport {
|
||||
shift;
|
||||
|
||||
# A bare C<no feature> should reset to the default bundle
|
||||
if (!@_) {
|
||||
$^H &= ~($hint_uni8bit|$hint_mask);
|
||||
return;
|
||||
}
|
||||
|
||||
__common(0, @_);
|
||||
}
|
||||
|
||||
|
||||
sub __common {
|
||||
my $import = shift;
|
||||
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, $^V));
|
||||
}
|
||||
|
||||
sub croak {
|
||||
require Carp;
|
||||
Carp::croak(@_);
|
||||
}
|
||||
|
||||
sub features_enabled {
|
||||
my ($depth) = @_;
|
||||
|
||||
$depth //= 1;
|
||||
my @frame = caller($depth+1)
|
||||
or return;
|
||||
my ($hints, $hinthash) = @frame[8, 10];
|
||||
|
||||
my $bundle_number = $hints & $hint_mask;
|
||||
if ($bundle_number != $hint_mask) {
|
||||
return $feature_bundle{$hint_bundles[$bundle_number >> $hint_shift]}->@*;
|
||||
}
|
||||
else {
|
||||
my @features;
|
||||
for my $feature (sort keys %feature) {
|
||||
if ($hinthash->{$feature{$feature}}) {
|
||||
push @features, $feature;
|
||||
}
|
||||
}
|
||||
return @features;
|
||||
}
|
||||
}
|
||||
|
||||
sub feature_enabled {
|
||||
my ($feature, $depth) = @_;
|
||||
|
||||
$depth //= 1;
|
||||
my @frame = caller($depth+1)
|
||||
or return;
|
||||
my ($hints, $hinthash) = @frame[8, 10];
|
||||
|
||||
my $hint_feature = $feature{$feature}
|
||||
or croak "Unknown feature $feature";
|
||||
my $bundle_number = $hints & $hint_mask;
|
||||
if ($bundle_number != $hint_mask) {
|
||||
my $bundle = $hint_bundles[$bundle_number >> $hint_shift];
|
||||
for my $bundle_feature ($feature_bundle{$bundle}->@*) {
|
||||
return 1 if $bundle_feature eq $feature;
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
else {
|
||||
return $hinthash->{$hint_feature} // 0;
|
||||
}
|
||||
}
|
||||
|
||||
sub feature_bundle {
|
||||
my $depth = shift;
|
||||
|
||||
$depth //= 1;
|
||||
my @frame = caller($depth+1)
|
||||
or return;
|
||||
my $bundle_number = $frame[8] & $hint_mask;
|
||||
if ($bundle_number != $hint_mask) {
|
||||
return $hint_bundles[$bundle_number >> $hint_shift];
|
||||
}
|
||||
else {
|
||||
return undef;
|
||||
}
|
||||
}
|
||||
|
||||
1;
|
||||
|
||||
# ex: set ro ft=perl:
|
||||
Loading…
Add table
Add a link
Reference in a new issue