mirror of
https://git.savannah.gnu.org/git/parallel.git
synced 2024-11-22 22:17:54 +00:00
250 lines
6.5 KiB
Perl
250 lines
6.5 KiB
Perl
package feature;
|
|
|
|
our $VERSION = '1.20';
|
|
|
|
# (feature name) => (internal name, used in %^H)
|
|
my %feature = (
|
|
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 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)],
|
|
"5.14" => [qw(switch say state unicode_strings)],
|
|
);
|
|
|
|
# special case
|
|
$feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
|
|
|
|
# TODO:
|
|
# - think about versioned features (use feature switch => 2)
|
|
|
|
=head1 NAME
|
|
|
|
feature - Perl pragma to enable new features
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
use feature qw(switch say);
|
|
given ($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" }
|
|
}
|
|
|
|
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, 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 Lexical effect
|
|
|
|
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.
|
|
|
|
{
|
|
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 '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 'say' feature
|
|
|
|
C<use feature 'say'> tells the compiler to enable the Perl 6
|
|
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 '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.
|
|
|
|
=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 {
|
|
my $class = shift;
|
|
if (@_ == 0) {
|
|
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;
|
|
$^H |= $hint_uni8bit if $name eq 'unicode_strings';
|
|
}
|
|
}
|
|
|
|
sub unimport {
|
|
my $class = shift;
|
|
|
|
# A bare C<no feature> should disable *all* features
|
|
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{$name})) {
|
|
unknown_feature($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;
|