diff options
Diffstat (limited to 'lib/feature.pm')
| -rw-r--r-- | lib/feature.pm | 174 |
1 files changed, 99 insertions, 75 deletions
diff --git a/lib/feature.pm b/lib/feature.pm index ac7a23c9c5..4cfa27ffdc 100644 --- a/lib/feature.pm +++ b/lib/feature.pm @@ -47,15 +47,17 @@ feature - Perl pragma to enable new features use feature qw(say switch); given ($foo) { - when (1) { say "\$foo == 1" } - when ([2,3]) { say "\$foo == 2 || \$foo == 3" } - when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } - when ($_ > 100) { say "\$foo > 100" } - default { say "None of the above" } + when (1) { say "\$foo == 1" } + when ([2,3]) { say "\$foo == 2 || \$foo == 3" } + when (/^a[bc]d$/) { 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 + use v5.10; # implicitly loads :5.10 feature bundle + =head1 DESCRIPTION It is usually impossible to add new syntax to Perl without breaking @@ -93,20 +95,26 @@ has lexical effect. C<no feature> with no features specified will turn off all features. +=head1 AVAILABLE FEATURES + =head2 The 'say' feature -C<use feature 'say'> tells the compiler to enable the Perl 6 +C<use feature 'say'> tells the compiler to enable the Perl 6 style C<say> function. See L<perlfunc/say> for details. -=head2 the 'state' feature +This feature is available starting with Perl 5.10. + +=head2 The 'state' feature C<use feature 'state'> tells the compiler to enable C<state> variables. See L<perlsub/"Persistent Private Variables"> for details. +This feature is available starting with Perl 5.10. + =head2 The 'switch' feature C<use feature 'switch'> tells the compiler to enable the Perl 6 @@ -114,7 +122,9 @@ given/when construct. See L<perlsyn/"Switch statements"> for details. -=head2 the 'unicode_strings' feature +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 in all string operations executed within its scope (unless they are also @@ -130,10 +140,10 @@ 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. +This feature is available starting with Perl 5.12, but was not fully +implemented until Perl 5.14. -=head2 the 'unicode_eval' and 'evalbytes' features +=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 @@ -189,45 +199,57 @@ This feature is available starting with Perl 5.16. =head1 FEATURE BUNDLES -It's possible to load a whole slew of features in one go, using +It's possible to load multiple features together, 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, most -feature bundles correspond to Perl releases, e.g. C<use feature -":5.10"> which is equivalent to C<use feature qw(switch say state)>. The -only bundle that does not follow this convention is ":default", which is -currently empty. - -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)>. +a colon, to distinguish it from an actual feature. + + use feature ":5.10"; + +The following feature bundles are available: + + bundle features included + --------- ----------------- + :default none + + :5.10 say state switch + + :5.12 say state switch unicode_strings + + :5.14 say state switch unicode_strings + + :5.16 say state switch unicode_strings + unicode_eval evalbytes current_sub + +The empty C<:default> bundle is provided for future +backwards-compatibility when using L<implicit loading|/IMPLICIT LOADING>. 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. +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. + use feature ":5.14.0"; # same as ":5.14" + use feature ":5.14.1"; # same as ":5.14" =head1 IMPLICIT LOADING -There are two ways to load the C<feature> pragma implicitly : +Instead of loading feature bundles by name, it is easier to let Perl do +implicit loading of a feature bundle for you. + +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.) +By using the C<-E> switch on the Perl command-line instead of C<-e>. +That will enable the feature bundle for that version of Perl in the +main compilation unit (that is, the one-liner that follows C<-E>). =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, +By explicitly requiring a minimum Perl version number for your program, with +the C<use VERSION> construct. That is, - use 5.10.0; + use v5.10.0; will do an implicit @@ -243,8 +265,10 @@ But to avoid portability warnings (see L<perlfunc/use>), you may prefer: with the same effect. -For versions below 5.010, the ":default" feature bundle is automatically -loaded, but it is currently empty and has no effect. +If the required version is older than Perl 5.10, the ":default" feature +bundle is automatically loaded instead. It is currently empty and has no +effect, but may be used in the future to support backwards +compatibility. =back @@ -253,25 +277,25 @@ loaded, but it is currently empty and has no effect. sub import { my $class = shift; if (@_ == 0) { - croak("No features specified"); + 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}) { - unknown_feature($name); - } - $^H{$feature{$name}} = 1; + 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}) { + unknown_feature($name); + } + $^H{$feature{$name}} = 1; $^H |= $hint_uni8bit if $name eq 'unicode_strings'; } } @@ -281,44 +305,44 @@ sub unimport { # A bare C<no feature> should disable *all* features if (!@_) { - delete @^H{ values(%feature) }; + delete @^H{ values(%feature) }; $^H &= ~ $hint_uni8bit; - return; + 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{$name})) { - unknown_feature($name); - } - else { - delete $^H{$feature{$name}}; + 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{$name})) { + unknown_feature($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)); + $feature, $^V)); } sub unknown_feature_bundle { my $feature = shift; croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', - $feature, $^V)); + $feature, $^V)); } sub croak { |