package feature;
-our $VERSION = '1.00';
-$feature::hint_bits = 0x04020000; # HINT_LOCALIZE_HH | HINT_HH_FOR_EVAL
+our $VERSION = '1.23';
# (feature name) => (internal name, used in %^H)
my %feature = (
- switch => 'feature_switch',
- "~~" => "feature_~~",
- say => "feature_say",
+ say => 'feature_say',
+ state => 'feature_state',
+ switch => 'feature_switch',
+ evalbytes => 'feature_evalbytes',
+ unicode_eval => 'feature_unieval',
+ unicode_strings => 'feature_unicode',
);
+# 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;
+
+# NB. the latest bundle must be loaded by the -E switch (see toke.c)
+
+our %feature_bundle = (
+ "5.10" => [qw(say state switch)],
+ "5.11" => [qw(say state switch unicode_strings)],
+ "5.15" => [qw(say state switch unicode_strings unicode_eval
+ evalbytes)],
+);
+
+# Each of these is the same as the previous bundle
+for(12...14, 16) {
+ $feature_bundle{"5.$_"} = $feature_bundle{"5.".($_-1)}
+}
+
+# special case
+$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
-# Here are some notes that probably shouldn't be in the public
-# documentation, but which it's useful to have somewhere.
-#
-# One side-effect of the change is that C<prototype("CORE::continue")>
-# no longer throws the error C<Can't find an opnumber for "continue">.
-# One of the tests in t/op/cproto.t had to be changed to accommodate
-# this, but it really shouldn't affect real-world code.
-#
# TODO:
-# - sort out the smartmatch semantics
-# - think about versioned features (use switch => 2)
-#
-# -- Robin 2005-12
+# - think about versioned features (use feature switch => 2)
=head1 NAME
-feature - Perl pragma to enable new syntactic features
+feature - Perl pragma to enable new features
=head1 SYNOPSIS
- use feature 'switch';
+ use feature qw(say switch);
given ($foo) {
- when (1) { print "\$foo == 1\n" }
- when ([2,3]) { print "\$foo == 2 || \$foo == 3\n" }
- when (/^a[bc]d$/) { print "\$foo eq 'abd' || \$foo eq 'acd'\n" }
- when ($_ > 100) { print "\$foo > 100\n" }
- default { print "None of the above\n" }
+ when (1) { say "\$foo == 1" }
+ when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
+ when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
+ when ($_ > 100) { say "\$foo > 100" }
+ default { say "None of the above" }
}
+ use feature ':5.10'; # loads all features available in perl 5.10
+
=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 can be enabled by C<use feature 'foo'>,
-and will be parsed only when the appropriate feature pragma is in
-scope.
+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 The 'switch' feature
+=head2 Lexical effect
-C<use feature 'switch'> tells the compiler to enable the Perl 6
-given/when construct from here to the end of the enclosing BLOCK.
+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.
-See L<perlsyn/"Switch statements"> for details.
+ {
+ use feature 'say';
+ say "say is available here";
+ }
+ print "But not here.\n";
+
+=head2 C<no feature>
-=head2 The '~~' feature
+Features can also be turned off by using C<no feature "foo">. This too
+has lexical effect.
-C<use feature '~~'> tells the compiler to enable the Perl 6
-smart match C<~~> operator from here to the end of the enclosing BLOCK.
+ use feature 'say';
+ say "say is available here";
+ {
+ no feature 'say';
+ print "But not here.\n";
+ }
+ say "Yet it is here.";
-See L<perlsyn/"Smart Matching in Detail"> for details.
+C<no feature> with no features specified will turn off all features.
=head2 The 'say' feature
C<use feature 'say'> tells the compiler to enable the Perl 6
-C<say> function from here to the end of the enclosing BLOCK.
+C<say> function.
See L<perlfunc/say> for details.
+=head2 the 'state' feature
+
+C<use feature 'state'> tells the compiler to enable C<state>
+variables.
+
+See L<perlsub/"Persistent Private Variables"> for details.
+
+=head2 The 'switch' feature
+
+C<use feature 'switch'> tells the compiler to enable the Perl 6
+given/when construct.
+
+See L<perlsyn/"Switch statements"> for details.
+
+=head2 the 'unicode_strings' feature
+
+C<use feature 'unicode_strings'> tells the compiler to use Unicode semantics
+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.
+
+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
+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 subpragma is available starting with Perl 5.11.3, but was not fully
+implemented until 5.13.8.
+
+=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.
+
+=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
+
+=back
+
+These two features are available starting with Perl 5.16.
+
+=head1 FEATURE BUNDLES
+
+It's possible to load a whole slew of features in one go, using
+a I<feature bundle>. The name of a feature bundle is prefixed with
+a colon, to distinguish it from an actual feature. At present, the
+only feature bundles correspond to Perl releases, e.g. C<use feature
+":5.10"> which is equivalent to C<use feature qw(switch say state)>.
+
+By convention, the feature bundle for any given Perl release includes
+the features of previous releases, down to and including 5.10, the
+first official release to provide this facility. Since Perl 5.12
+only provides one new feature, C<unicode_strings>, and Perl 5.14
+provides none, C<use feature ":5.14"> is equivalent to C<use feature
+qw(switch say state unicode_strings)>.
+
+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.
+
+Note that instead of using release-based feature bundles it is usually
+better, and shorter, to use implicit loading as described below.
+
+=head1 IMPLICIT LOADING
+
+There are two ways to load the C<feature> pragma implicitly :
+
+=over 4
+
+=item *
+
+By using the C<-E> switch on the command-line instead of C<-e>. It enables
+all available features in the main compilation unit (that is, the one-liner.)
+
+=item *
+
+By requiring explicitly a minimal Perl version number for your program, with
+the C<use VERSION> construct, and when the version is higher than or equal to
+5.10.0. That is,
+
+ use 5.10.0;
+
+will do an implicit
+
+ use feature ':5.10';
+
+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 5.010;
+
+with the same effect.
+
+=back
+
=cut
sub import {
- $^H |= $feature::hint_bits; # Need this or %^H won't work
-
my $class = shift;
if (@_ == 0) {
- require Carp;
- Carp->import("croak");
croak("No features specified");
}
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}) {
- require Carp;
- Carp->import("croak");
- croak(sprintf('Feature "%s" is not supported by Perl %vd',
- $name, $^V));
+ unknown_feature($name);
}
$^H{$feature{$name}} = 1;
+ $^H |= $hint_uni8bit if $name eq 'unicode_strings';
}
}
my $class = shift;
# A bare C<no feature> should disable *all* features
- for my $name (@_) {
+ if (!@_) {
+ delete @^H{ values(%feature) };
+ $^H &= ~ $hint_uni8bit;
+ return;
+ }
+
+ 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})) {
- require Carp;
- Carp->import("croak");
- croak(sprintf('Feature "%s" is not supported by Perl %vd',
- $name, $^V));
+ unknown_feature($name);
}
else {
delete $^H{$feature{$name}};
+ $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings';
}
}
+}
- if(!@_) {
- delete @^H{ values(%feature) };
- }
+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;
https://perl5.git.perl.org / perl5.git / blobdiff