1package experimental; 2$experimental::VERSION = '0.016'; 3use strict; 4use warnings; 5use version (); 6 7use feature (); 8use Carp qw/croak carp/; 9 10my %warnings = map { $_ => 1 } grep { /^experimental::/ } keys %warnings::Offsets; 11my %features = map { $_ => 1 } $] > 5.015006 ? keys %feature::feature : do { 12 my @features; 13 if ($] >= 5.010) { 14 push @features, qw/switch say state/; 15 push @features, 'unicode_strings' if $] > 5.011002; 16 } 17 @features; 18}; 19 20my %min_version = ( 21 array_base => '5', 22 autoderef => '5.14.0', 23 bitwise => '5.22.0', 24 current_sub => '5.16.0', 25 evalbytes => '5.16.0', 26 fc => '5.16.0', 27 lexical_topic => '5.10.0', 28 lexical_subs => '5.18.0', 29 postderef => '5.20.0', 30 postderef_qq => '5.20.0', 31 refaliasing => '5.22.0', 32 regex_sets => '5.18.0', 33 say => '5.10.0', 34 smartmatch => '5.10.0', 35 signatures => '5.20.0', 36 state => '5.10.0', 37 switch => '5.10.0', 38 unicode_eval => '5.16.0', 39 unicode_strings => '5.12.0', 40); 41my %max_version = ( 42 lexical_topic => '5.23.4', 43); 44 45$_ = version->new($_) for values %min_version; 46$_ = version->new($_) for values %max_version; 47 48my %additional = ( 49 postderef => ['postderef_qq'], 50 switch => ['smartmatch'], 51); 52 53sub _enable { 54 my $pragma = shift; 55 if ($warnings{"experimental::$pragma"}) { 56 warnings->unimport("experimental::$pragma"); 57 feature->import($pragma) if exists $features{$pragma}; 58 _enable(@{ $additional{$pragma} }) if $additional{$pragma}; 59 } 60 elsif ($features{$pragma}) { 61 feature->import($pragma); 62 _enable(@{ $additional{$pragma} }) if $additional{$pragma}; 63 } 64 elsif (not exists $min_version{$pragma}) { 65 croak "Can't enable unknown feature $pragma"; 66 } 67 elsif ($] < $min_version{$pragma}) { 68 my $stable = $min_version{$pragma}; 69 if ($stable->{version}[1] % 2) { 70 $stable = version->new( 71 "5.".($stable->{version}[1]+1).'.0' 72 ); 73 } 74 croak "Need perl $stable or later for feature $pragma"; 75 } 76 elsif ($] >= ($max_version{$pragma} || 7)) { 77 croak "Experimental feature $pragma has been removed from perl in version $max_version{$pragma}"; 78 } 79} 80 81sub import { 82 my ($self, @pragmas) = @_; 83 84 for my $pragma (@pragmas) { 85 _enable($pragma); 86 } 87 return; 88} 89 90sub _disable { 91 my $pragma = shift; 92 if ($warnings{"experimental::$pragma"}) { 93 warnings->import("experimental::$pragma"); 94 feature->unimport($pragma) if exists $features{$pragma}; 95 _disable(@{ $additional{$pragma} }) if $additional{$pragma}; 96 } 97 elsif ($features{$pragma}) { 98 feature->unimport($pragma); 99 _disable(@{ $additional{$pragma} }) if $additional{$pragma}; 100 } 101 elsif (not exists $min_version{$pragma}) { 102 carp "Can't disable unknown feature $pragma, ignoring"; 103 } 104} 105 106sub unimport { 107 my ($self, @pragmas) = @_; 108 109 for my $pragma (@pragmas) { 110 _disable($pragma); 111 } 112 return; 113} 114 1151; 116 117#ABSTRACT: Experimental features made easy 118 119__END__ 120 121=pod 122 123=encoding UTF-8 124 125=head1 NAME 126 127experimental - Experimental features made easy 128 129=head1 VERSION 130 131version 0.016 132 133=head1 SYNOPSIS 134 135 use experimental 'lexical_subs', 'smartmatch'; 136 my sub foo { $_[0] ~~ 1 } 137 138=head1 DESCRIPTION 139 140This pragma provides an easy and convenient way to enable or disable 141experimental features. 142 143Every version of perl has some number of features present but considered 144"experimental." For much of the life of Perl 5, this was only a designation 145found in the documentation. Starting in Perl v5.10.0, and more aggressively in 146v5.18.0, experimental features were placed behind pragmata used to enable the 147feature and disable associated warnings. 148 149The C<experimental> pragma exists to combine the required incantations into a 150single interface stable across releases of perl. For every experimental 151feature, this should enable the feature and silence warnings for the enclosing 152lexical scope: 153 154 use experimental 'feature-name'; 155 156To disable the feature and, if applicable, re-enable any warnings, use: 157 158 no experimental 'feature-name'; 159 160The supported features, documented further below, are: 161 162 array_base - allow the use of $[ to change the starting index of @array 163 autoderef - allow push, each, keys, and other built-ins on references 164 lexical_topic - allow the use of lexical $_ via "my $_" 165 postderef - allow the use of postfix dereferencing expressions, including 166 in interpolating strings 167 refaliasing - allow aliasing via \$x = \$y 168 regex_sets - allow extended bracketed character classes in regexps 169 signatures - allow subroutine signatures (for named arguments) 170 smartmatch - allow the use of ~~ 171 switch - allow the use of ~~, given, and when 172 173=head2 Ordering matters 174 175Using this pragma to 'enable an experimental feature' is another way of saying 176that this pragma will disable the warnings which would result from using that 177feature. Therefore, the order in which pragmas are applied is important. In 178particular, you probably want to enable experimental features I<after> you 179enable warnings: 180 181 use warnings; 182 use experimental 'smartmatch'; 183 184You also need to take care with modules that enable warnings for you. A common 185example being Moose. In this example, warnings for the 'smartmatch' feature are 186first turned on by the warnings pragma, off by the experimental pragma and back 187on again by the Moose module (fix is to switch the last two lines): 188 189 use warnings; 190 use experimental 'smartmatch'; 191 use Moose; 192 193=head2 Disclaimer 194 195Because of the nature of the features it enables, forward compatibility can not 196be guaranteed in any way. 197 198=head1 AUTHOR 199 200Leon Timmermans <leont@cpan.org> 201 202=head1 COPYRIGHT AND LICENSE 203 204This software is copyright (c) 2013 by Leon Timmermans. 205 206This is free software; you can redistribute it and/or modify it under 207the same terms as the Perl 5 programming language system itself. 208 209=cut 210