X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/64fbf0dd43246bda0d854a4cbf1884b785d4d890..b6dbf1d39057ebab301f6e56d7c7ebcd44cefe8b:/lib/feature.pm

diff --git a/lib/feature.pm b/lib/feature.pm
index 7654821..668b430 100644
--- a/lib/feature.pm
+++ b/lib/feature.pm
@@ -5,27 +5,33 @@
 
 package feature;
 
-our $VERSION = '1.31';
+our $VERSION = '1.57';
 
 our %feature = (
     fc              => 'feature_fc',
+    isa             => 'feature_isa',
     say             => 'feature_say',
     state           => 'feature_state',
     switch          => 'feature_switch',
+    bitwise         => 'feature_bitwise',
     evalbytes       => 'feature_evalbytes',
-    array_base      => 'feature_arybase',
+    signatures      => 'feature_signatures',
     current_sub     => 'feature___SUB__',
-    lexical_subs    => 'feature_lexsubs',
+    refaliasing     => 'feature_refaliasing',
+    postderef_qq    => 'feature_postderef_qq',
     unicode_eval    => 'feature_unieval',
+    declared_refs   => 'feature_myref',
     unicode_strings => 'feature_unicode',
 );
 
 our %feature_bundle = (
-    "5.10"    => [qw(array_base say state switch)],
-    "5.11"    => [qw(array_base say state switch unicode_strings)],
+    "5.10"    => [qw(say state switch)],
+    "5.11"    => [qw(say state switch unicode_strings)],
     "5.15"    => [qw(current_sub evalbytes fc say state switch unicode_eval unicode_strings)],
-    "all"     => [qw(array_base current_sub evalbytes fc lexical_subs say state switch unicode_eval unicode_strings)],
-    "default" => [qw(array_base)],
+    "5.23"    => [qw(current_sub evalbytes fc postderef_qq say state switch unicode_eval unicode_strings)],
+    "5.27"    => [qw(bitwise current_sub evalbytes fc postderef_qq say state switch unicode_eval unicode_strings)],
+    "all"     => [qw(bitwise current_sub declared_refs evalbytes fc isa postderef_qq refaliasing say signatures state switch unicode_eval unicode_strings)],
+    "default" => [qw()],
 );
 
 $feature_bundle{"5.12"} = $feature_bundle{"5.11"};
@@ -34,11 +40,30 @@ $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{"5.9.5"} = $feature_bundle{"5.10"};
+my %noops = (
+    postderef => 1,
+    lexical_subs => 1,
+);
+my %removed = (
+    array_base => 1,
+);
 
 our $hint_shift   = 26;
 our $hint_mask    = 0x1c000000;
-our @hint_bundles = qw( default 5.10 5.11 5.15 );
+our @hint_bundles = qw( default 5.10 5.11 5.15 5.23 5.27 );
 
 # This gets set (for now) in $^H as well as in %^H,
 # for runtime speed of the uc/lc/ucfirst/lcfirst functions.
@@ -127,6 +152,12 @@ This feature is available starting with Perl 5.10.
 
 =head2 The 'switch' feature
 
+B<WARNING>: Because the L<smartmatch operator|perlop/"Smartmatch Operator"> is
+experimental, Perl will warn when you use this feature, unless you have
+explicitly disabled the warning:
+
+    no warnings "experimental::smartmatch";
+
 C<use feature 'switch'> tells the compiler to enable the Perl 6
 given/when construct.
 
@@ -136,7 +167,7 @@ This feature is available starting with Perl 5.10.
 
 =head2 The 'unicode_strings' feature
 
-C<use feature 'unicode_strings'> tells the compiler to use Unicode semantics
+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
@@ -144,7 +175,7 @@ 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 semantics wherein the native character set semantics is used unless it is
+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
@@ -152,54 +183,29 @@ 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>.
+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
 
-Under the C<unicode_eval> feature, Perl's C<eval> function, when passed a
-string, will evaluate it as a string of characters, ignoring any
-C<use utf8> declarations.  C<use utf8> exists to declare the encoding of
-the script, which only makes sense for a stream of bytes, not a string of
-characters.  Source filters are forbidden, as they also really only make
-sense on strings of bytes.  Any attempt to activate a source filter will
-result in an error.
-
-The C<evalbytes> feature enables the C<evalbytes> keyword, which evaluates
-the argument passed to it as a string of bytes.  It dies if the string
-contains any characters outside the 8-bit range.  Source filters work
-within C<evalbytes>: they apply to the contents of the string being
-evaluated.
-
-Together, these two features are intended to replace the historical C<eval>
-function, which has (at least) two bugs in it, that cannot easily be fixed
-without breaking existing programs:
-
-=over
-
-=item *
-
-C<eval> behaves differently depending on the internal encoding of the
-string, sometimes treating its argument as a string of bytes, and sometimes
-as a string of characters.
+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.
 
-=item *
-
-Source filters activated within C<eval> leak out into whichever I<file>
-scope is currently being compiled.  To give an example with the CPAN module
-L<Semi::Semicolons>:
-
-    BEGIN { eval "use Semi::Semicolons;  # not filtered here " }
-    # filtered here!
-
-C<evalbytes> fixes that to work the way one would expect:
-
-    use feature "evalbytes";
-    BEGIN { evalbytes "use Semi::Semicolons;  # filtered " }
-    # not filtered
+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>.
 
-=back
-
-These two features are available starting with Perl 5.16.
+C<evalbytes> is like string C<eval>, but operating on a byte stream that is
+not UTF-8 encoded.  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
 
@@ -210,9 +216,9 @@ This feature is available starting with Perl 5.16.
 
 =head2 The 'array_base' feature
 
-This feature supports the legacy C<$[> variable.  See L<perlvar/$[> and
-L<arybase>.  It is on by default but disabled under C<use v5.16> (see
-L</IMPLICIT LOADING>, below).
+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
@@ -229,17 +235,129 @@ 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
+and scalar dereference 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
+
 B<WARNING>: This feature is still experimental and the implementation may
 change 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::lexical_subs";
+    no warnings "experimental::signatures";
 
-This enables 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 enables unpacking of subroutine arguments into lexical variables
+by syntax such as
+
+    sub foo ($left, $right) {
+	return $left + $right;
+    }
+
+See L<perlsub/Signatures> for details.
+
+This feature is available from Perl 5.20 onwards.
 
-This feature is available from Perl 5.18 onwards.
+=head2 The 'refaliasing' feature
+
+B<WARNING>: This feature is still experimental and the implementation may
+change 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 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>,
+our 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.
 
 =head1 FEATURE BUNDLES
 
@@ -253,13 +371,13 @@ The following feature bundles are available:
 
   bundle    features included
   --------- -----------------
-  :default  array_base
+  :default
 
-  :5.10     say state switch array_base
+  :5.10     say state switch
 
-  :5.12     say state switch unicode_strings array_base
+  :5.12     say state switch unicode_strings
 
-  :5.14     say state switch unicode_strings array_base
+  :5.14     say state switch unicode_strings
 
   :5.16     say state switch unicode_strings
             unicode_eval evalbytes current_sub fc
@@ -267,6 +385,32 @@ The following feature bundles are available:
   :5.18     say state switch unicode_strings
             unicode_eval evalbytes current_sub fc
 
+  :5.20     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+
+  :5.22     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+
+  :5.24     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+            postderef_qq
+
+  :5.26     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+            postderef_qq
+
+  :5.28     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+            postderef_qq bitwise
+
+  :5.30     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+            postderef_qq bitwise
+
+  :5.32     say state switch unicode_strings
+            unicode_eval evalbytes current_sub fc
+            postderef_qq bitwise
+
 The C<:default> bundle represents the feature set that is enabled before
 any C<use feature> or C<no feature> declaration.
 
@@ -316,12 +460,15 @@ 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
 
 =cut
 
 sub import {
-    my $class = shift;
+    shift;
 
     if (!@_) {
         croak("No features specified");
@@ -331,7 +478,7 @@ sub import {
 }
 
 sub unimport {
-    my $class = shift;
+    shift;
 
     # A bare C<no feature> should reset to the default bundle
     if (!@_) {
@@ -347,7 +494,7 @@ 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]};
+      && $feature_bundle{$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.
@@ -372,6 +519,12 @@ sub __common {
             next;
         }
         if (!exists $feature{$name}) {
+            if (exists $noops{$name}) {
+                next;
+            }
+            if (!$import && exists $removed{$name}) {
+                next;
+            }
             unknown_feature($name);
         }
 	if ($import) {