X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/5b9c067131ee63b4afa00d1d71c771377deb6ff9..789bd863840ef4ff6c46f7c2ee0f3f64e0b5daa6:/lib/feature.pm

diff --git a/lib/feature.pm b/lib/feature.pm
index d4975e4..3cf838a 100644
--- a/lib/feature.pm
+++ b/lib/feature.pm
@@ -1,37 +1,38 @@
 package feature;
 
-our $VERSION = '1.00';
+our $VERSION = '1.17';
 
 # (feature name) => (internal name, used in %^H)
 my %feature = (
-    switch => 'feature_switch',
-    "~~"   => "feature_~~",
-    say    => "feature_say",
-    err    => "feature_err",
+    switch          => 'feature_switch',
+    say             => "feature_say",
+    state           => "feature_state",
+    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)
+
 my %feature_bundle = (
-    "5.10" => [qw(switch ~~ say err)],
+    "5.10" => [qw(switch say state)],
+    "5.11" => [qw(switch say state unicode_strings)],
+    "5.12" => [qw(switch say state unicode_strings)],
+    "5.13" => [qw(switch say state unicode_strings)],
 );
 
+# 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
 
@@ -44,79 +45,142 @@ feature - Perl pragma to enable new syntactic features
 	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.
 
-=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.";
 
-=head2 The '~~' feature
+C<no feature> with no features specified will turn off all features.
 
-C<use feature '~~'> tells the compiler to enable the Perl 6
-smart match C<~~> operator from here to the end of the enclosing BLOCK.
+=head2 The 'switch' feature
 
-See L<perlsyn/"Smart Matching in Detail"> for details.
+C<use feature 'switch'> tells the compiler to enable the Perl 6
+given/when construct.
+
+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 'err' feature
+=head2 the 'state' feature
 
-C<use feature 'err'> tells the compiler to enable the C<err>
-operator from here to the end of the enclosing BLOCK.
+C<use feature 'state'> tells the compiler to enable C<state>
+variables.
 
-C<err> is a low-precedence variant of the C<//> operator:
-see C<perlop> for details.
+See L<perlsub/"Persistent Private Variables"> for details.
+
+=head2 the 'unicode_strings' feature
+
+C<use feature 'unicode_strings'> tells the compiler to treat
+all strings outside of C<use locale> and C<use bytes> as Unicode. It is
+available starting with Perl 5.11.3.
+
+See L<perlunicode/The "Unicode Bug"> 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 err)>.
+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 {
     my $class = shift;
     if (@_ == 0) {
-	require Carp;
-	Carp->import("croak");
 	croak("No features specified");
     }
     while (@_) {
 	my $name = shift(@_);
-	if ($name =~ /^:(.*)/) {
-	    if (!exists $feature_bundle{$1}) {
-		require Carp;
-		Carp->import("croak");
-		croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
-		    $1, $^V));
+	if (substr($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{$1}};
+	    unshift @_, @{$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';
     }
 }
 
@@ -126,31 +190,48 @@ sub unimport {
     # A bare C<no feature> should disable *all* features
     if (!@_) {
 	delete @^H{ values(%feature) };
+        $^H &= ~ $hint_uni8bit;
 	return;
     }
 
     while (@_) {
 	my $name = shift;
-	if ($name =~ /^:(.*)/) {
-	    if (!exists $feature_bundle{$1}) {
-		require Carp;
-		Carp->import("croak");
-		croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
-		    $1, $^V));
+	if (substr($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{$1}};
+	    unshift @_, @{$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';
 	}
     }
 }
 
+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;