package feature;
-our $VERSION = '1.01';
+our $VERSION = '1.10';
# (feature name) => (internal name, used in %^H)
my %feature = (
switch => 'feature_switch',
- "~~" => "feature_~~",
say => "feature_say",
err => "feature_err",
- dor => "feature_err",
state => "feature_state",
);
my %feature_bundle = (
- "5.10" => [qw(switch ~~ say err state)],
+ "5.10.0" => [qw(switch say err state)],
);
+# latest version here
+# keep it harcoded until we actually bump the version number to 5.10
+$feature_bundle{"5.10"} = $feature_bundle{"5.10.0"};
+#$feature_bundle{"5.10"} = $feature_bundle{sprintf("%vd",$^V)};
+$feature_bundle{"5.9.5"} = $feature_bundle{"5.10.0"};
# TODO:
# - think about versioned features (use feature switch => 2)
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.
-=head2 The '~~' feature
+ 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.
-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
C<use feature 'err'> tells the compiler to enable the C<err>
-operator from here to the end of the enclosing BLOCK.
+operator.
C<err> is a low-precedence variant of the C<//> operator:
see C<perlop> for details.
-=head2 the 'dor' feature
-
-The 'dor' feature is an alias for the 'err' feature.
-
=head2 the 'state' feature
C<use feature 'state'> tells the compiler to enable C<state>
-variables from here to the end of the enclosing BLOCK.
+variables.
See L<perlsub/"Persistent Private Variables"> for details.
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 state)>.
+only feature bundles are C<use feature ":5.10"> and C<use feature ":5.10.0">,
+which both are equivalent to C<use feature qw(switch say err state)>.
+
+In the forthcoming 5.10.X perl releases, C<use feature ":5.10"> will be
+equivalent to the latest C<use feature ":5.10.X">.
+
+=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
+5.9.5. That is,
+
+ use 5.9.5;
+
+will do an implicit
+
+ use feature ':5.9.5';
+
+and so on.
+
+=back
=cut
}
while (@_) {
my $name = shift(@_);
- if ($name =~ /^:(.*)/) {
- if (!exists $feature_bundle{$1}) {
- unknown_feature_bundle($1);
+ if (substr($name, 0, 1) eq ":") {
+ my $v = substr($name, 1);
+ if (!exists $feature_bundle{$v}) {
+ unknown_feature_bundle($v);
}
- unshift @_, @{$feature_bundle{$1}};
+ unshift @_, @{$feature_bundle{$v}};
next;
}
if (!exists $feature{$name}) {
while (@_) {
my $name = shift;
- if ($name =~ /^:(.*)/) {
- if (!exists $feature_bundle{$1}) {
- unknown_feature_bundle($1);
+ if (substr($name, 0, 1) eq ":") {
+ my $v = substr($name, 1);
+ if (!exists $feature_bundle{$v}) {
+ unknown_feature_bundle($v);
}
- unshift @_, @{$feature_bundle{$1}};
+ unshift @_, @{$feature_bundle{$v}};
next;
}
if (!exists($feature{$name})) {