package feature;
-our $VERSION = '1.00';
-$feature::hint_bits = 0x04020000; # HINT_LOCALIZE_HH | HINT_HH_FOR_EVAL
+our $VERSION = '1.13';
# (feature name) => (internal name, used in %^H)
my %feature = (
switch => 'feature_switch',
- "~~" => "feature_~~",
say => "feature_say",
+ state => "feature_state",
);
+# NB. the latest bundle must be loaded by the -E switch (see toke.c)
+
+my %feature_bundle = (
+ "5.10" => [qw(switch say state)],
+ "5.11" => [qw(switch say state)],
+);
+
+# special case
+$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
-# Here are some notes that probably shouldn't be in the public
-# documentation, but which it's useful to have somewhere.
-#
-# One side-effect of the change is that C<prototype("CORE::continue")>
-# no longer throws the error C<Can't find an opnumber for "continue">.
-# One of the tests in t/op/cproto.t had to be changed to accommodate
-# this, but it really shouldn't affect real-world code.
-#
# TODO:
-# - sort out the smartmatch semantics
-# - think about versioned features (use switch => 2)
-#
-# -- Robin 2005-12
+# - think about versioned features (use feature switch => 2)
=head1 NAME
=head1 SYNOPSIS
- use feature 'switch';
+ use feature qw(switch say);
given ($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
and will be parsed only when the appropriate feature pragma is in
scope.
-=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>
+
+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 turn off all features.
-=head2 The '~~' feature
+=head2 The 'switch' feature
-C<use feature '~~'> tells the compiler to enable the Perl 6
-smart match C<~~> operator from here to the end of the enclosing BLOCK.
+C<use feature 'switch'> tells the compiler to enable the Perl 6
+given/when construct.
-See L<perlsyn/"Smart Matching in Detail"> for details.
+See L<perlsyn/"Switch statements"> for details.
=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.
+
+=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 bundle is C<use feature ":5.10"> which is equivalent
+to C<use feature qw(switch say state)>.
+
+Specifying sub-versions such as the C<0> in C<5.10.0> in feature bundles has
+no effect: feature bundles are guaranteed to be the same for all sub-versions.
+
+=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;
}
my $class = shift;
# A bare C<no feature> should disable *all* features
- for my $name (@_) {
+ if (!@_) {
+ delete @^H{ values(%feature) };
+ 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}};
}
}
+}
- 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;
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