File Coverage

blib/lib/Syntax/Construct.pm

Criterion	Covered	Total	%
statement	50	58	86.2
branch	27	36	75.0
condition	6	11	54.5
subroutine	14	15	93.3
pod	2	2	100.0
total	99	122	81.1

package Syntax::Construct;

use 5.006002;
use strict;
use warnings;

our $VERSION = '1.045';

my %introduces = do { no warnings 'qw';
                 ( '5.042' => [qw[
                                  :writer my_method ->& unicode16.0 ^^=
                             ]],
                   '5.040' => [qw[
                                  ^^ __CLASS__ :reader
                             ]],
                   '5.038' => [qw[
                                 unicode15.0 ^HOOK signature-default-operator
                                 INCDIR *{} REG_INF_I32_MAX
                                 ^LAST_SUCCESSFUL_PATTERN
                             ]],
                   '5.036' => [qw[
                                 unicode14.0
                             ]],
                   '5.034' => [qw[
                                 {,n} 0o blanks-in-curlies
                             ]],
                   '5.032' => [qw[
                                  unicode13.0 chained-comparisons
                                  unicode-identifier-status
                                  unicode-name-property
                             ]],
                   '5.030' => [qw[
                                  unicode12.1 uniprop_wildcards qr'N
                                  turkic-casing ^RE_COMPILE_RECURSION_LIMIT
                             ]],
                   '5.028' => [qw[
                                 delete% unicode10.0 state@=
                             ]],
                   '5.026' => [qw[
                                 <<~ /xx ^CAPTURE unicode9.0 unicode-scx scalar%
                              ]],
                   '5.024' => [qw[
                                 unicode8.0 \b{lb} sprintf-reorder
                              ]],
                   '5.022' => [qw[
                                 <<>> \b{} /n unicode7.0 attr-const
                                 fileno-dir ()x= hexfloat chr-inf
                                 empty-slice /x-unicode
                              ]],
                   '5.020' => [qw[
                                 attr-prototype drand48 %slice
                                 unicode6.3 \p{Unicode} utf8-locale
                                 s-utf8-delimiters
                              ]],
                   '5.018' => [qw[
                                 computed-labels while-each method-on-any-string
                                 split-space
                              ]],
                   '5.016' => [qw[
                                 charnames __FILE__()
                              ]],
                   '5.014' => [qw[
                                 ?^ /r /d /l /u /a auto-deref
                                 ^GLOBAL_PHASE \o package-block
                                 srand-return prototype+ sig-warn-obj
                              ]],
                   '5.012' => [qw[
                                 package-version ... each-array
                                 keys-array values-array delete-local
                                 length-undef \N while-readdir
                              ]],
                   '5.010' => [qw[
                                 // ?PARNO ?<> ?| quant+ regex-verbs
                                 \K \R \v \h \gN readline()
                                 stack-file-test recursive-sort /p
                                 lexical-$_ pack<
                              ]],
                   '5.008001' => [qw[
                                 s-utf8-delimiters-hack
                              ]],
                   old => [qw[
                                 ?? for-qw @_=split no-sigil
                          ]],
                 )};

my %removed = ( 'auto-deref'             => '5.024',
                'lexical-$_'             => '5.024',
                '??'                     => '5.022',
                'no-sigil'               => '5.022',
                's-utf8-delimiters-hack' => '5.020',
                'for-qw'                 => '5.018',
                '@_=split'               => '5.012',
              );

my %alias = (
    # old
    'split-populates-@_' => '@_=split',
    # 5.010
    '\H' => '\h',
    '\V' => '\v',
    'defined-or' => '//',
    'lexical-default-variable' => 'lexical-$_',
    'pack-byte-order-modifiers' => 'pack<',
    'readline-argv' => 'readline()',
    'regex-generic-linebreak' => '\R',
    'regex-horizontal-whitespace' => '\h',
    'regex-keep-left' => '\K',
    'regex-named-capture-group' => '?<>',
    'regex-possessive-quantifier' => 'quant+',
    'regex-possessive-match' => 'quant+',
    'regex-preserve-match-captures' => '/p',
    'regex-recursive-subpattern' => '?PARNO',
    'regex-relative-backreference' => '\gN',
    'regex-reset-branch' => '?|',
    'regex-vertical-whitespace' => '\v',
    # 5.012
    'statement-ellipsis' => '...',
    'yada-yada' => '...',
    'triple-dot' => '...',
    'regex-non-newline' => '\N',
    # 5.014
    'non-destructive-subst' => '/r',
    'non-destructive-substitution' => '/r',
    'regex-restrict-ascii-range' => '/a',
    'regex-unicode-strings' => '/u',
    'regex-use-default-modifiers' => '?^',
    'regex-compile-as-default' => '/d',
    'regex-compile-as-locale' => '/l',
    'regex-compile-as-unicode-strings' => '/u',
    'global-phase' => '^GLOBAL_PHASE',
    'octal-escape' => '\o',
    # 5.016
    '__LINE__()' => '__FILE__()',
    '__PACKAGE__()' => '__FILE__()',
    # 5.020
    'hash-slice' => '%slice',
    'attribute-prototype' => 'attr-prototype',
    'regex-property-unicode' => '\p{Unicode}',
    'wide-char-delimiters' => 's-utf8-delimiters',
    'unicode-6.3' => 'unicode6.3',
    # 5.022
    'double-diamond' => '<<>>',
    'operator-double-diamond' => '<<>>',
    'regex-non-capturing' => '/n',
    '\b{gcb}' => '\b{}',
    '\b{wb}' => '\b{}',
    '\b{sb}' => '\b{}',
    'regex-unicode-boundary' => '\b{}',
    'regex-unicode-grapheme-cluster-boundary' => '\b{}',
    'regex-unicode-word-boundary' => '\b{}',
    'regex-unicode-sentence-boundary' => '\b{}',
    'attribute-const' => 'attr-const',
    'list-repetition-assignment' => '()x=',
    'hexadecimal-floating-numbers' => 'hexfloat',
    'pack-inf' => 'chr-inf',
    'regex-x-unicode' => '/x-unicode',
    'regex-x-handles-unicode' => '/x-unicode',
    'unicode-7.0' => 'unicode7.0',
    # 5.024
    'unicode-8.0' => 'unicode8.0',
    'regex-unicode-line-break-boundary' => '\b{lb}',
    'printf-precision-argument-reorder' => 'sprintf-reorder',
    'sprintf-precision-argument-reorder' => 'sprintf-reorder',
    # 5.026
    'unicode-9.0' => 'unicode9.0',
    'heredoc-indent' => '<<~',
    'regex-xx' => '/xx',
    'capture-variable' => '^CAPTURE',
    'scalar-hash' => 'scalar%',
    # 5.028
    'hash-delete-slice' => 'delete%',
    'unicode-10.0' => 'unicode10.0',
    'state-array' => 'state@=',
    'state-hash' => 'state@=',
    'list-context-state' => 'state@=',
    # 5.030
    'named-char-in-single-quoted-regex' => "qr'N",
    'unicode-12.1' => 'unicode12.1',
    're-compile-recursion-limit' => '^RE_COMPILE_RECURSION_LIMIT',
    # 5.032
    'unicode-13.0' => 'unicode13.0',
    'unicode-identifier-type' => 'unicode-identifier-status',
    # 5.034
    'empty-left-quantifier' => '{,n}',
    'octal-literals' => '0o',
    # 5.038
    'keyword-hook' => '^HOOK',
    'optimistic-eval' => '*{}',
    # 5.040
    'logical-xor' => '^^',
    # 5.042
    'lexical-method-invocation-operator' => '->&',
    'assign-logical-xor' => '^^=',
);

my %_introduced = map {
    my $version = $_;
    map { $_ => $version } @{ $introduces{$version} }
} keys %introduces;

my %introduced = %_introduced;
delete @introduced{ @{ $introduces{old} } };

sub _hook {
    { drand48 => sub {
          require Config;
          warn "Unknown rand implementation at ", _position(1), ".\n"
              unless 'Perl_drand48' eq $Config::Config{randfunc};
      },
      'turkic-casing' => sub {
          eval {
              use locale;
              require POSIX;
              my $orig_locale = POSIX::setlocale(POSIX::LC_CTYPE());
              (POSIX::setlocale(POSIX::LC_CTYPE(), 'tr_TR.UTF-8') || "")
                  eq 'tr_TR.UTF-8' or die;
              my $cmp = lc 'I' ne 'i';
              POSIX::setlocale(POSIX::LC_CTYPE(), $orig_locale);
              $cmp
          } or die 'Turkic locale casing not working at '
              . _position(1) . "\.\n";
      },
    }
}


sub removed {
    my $construct = shift;
    return $construct
        ? $removed{$construct}
            || $alias{$construct} && $removed{ $alias{$construct} }
        : keys %removed
}


sub introduced {
    my $construct = shift;
    return $construct
        ? $introduced{$construct}
            || $alias{$construct} && $introduced{ $alias{$construct} }
        : keys %introduced
}


sub _position {
    join ' line ', (caller(1 + !! shift))[1,2]
}


sub import {
    shift;
    my $min_version = 0;
    my $max_version = 6;
    my ($constr, $d_constr);
    my @actions;
    for my $name (@_) {
        local $_ = exists $alias{$name} ? $alias{$name} : $name;
        if ($introduced{$_}) {
            ($min_version, $constr) = ($introduced{$_}, $name)
                if $introduced{$_} gt $min_version;
        } elsif (! $removed{$_}) {
            die "Unknown construct `$name' at ",
                _position(),
                ". Try upgrading Syntax::Construct first.\n"
        }

        if ($removed{$_}) {
            ($max_version, $d_constr) = ($removed{$_}, $name)
                if $removed{$_} lt $max_version;
        }

        my $action = _hook()->{$_};
        push @actions, $action if $action;
    }
    die 'Empty construct list at ', _position(), ".\n" unless @_;

    my $nearest_stable = _nearest_stable();
    if ($max_version le $nearest_stable) {
        warn "Faking version $nearest_stable to test removed constructs.\n"
            if ! _is_stable($]) && $max_version eq $nearest_stable;
        die "$d_constr removed in $max_version at ", _position(), ".\n";
    }

    die "Unsupported construct $constr at ", _position(),
        sprintf " (Perl %s needed)\n", $min_version
        unless $min_version le $];

    $_->() for @actions;
}


sub _is_stable {
    my ($version) = @_;
    return $version =~ /^[0-5]\.[0-9][0-9][02468]/
}

sub _nearest_stable {
    return $] if _is_stable($]);
    my ($major, $minor) = $] =~ /^([0-5])\.([0-9][0-9][13579])/;
    ++$minor;
    return "$major.$minor"
}


sub _is_old_empty { @{ $introduces{old} } ? 0 : 1 }


=head1 NAME

Syntax::Construct - Explicitly state which non-feature constructs are used in the code.

=head1 VERSION

Version 1.045

=head1 SYNOPSIS

For some new syntactic constructs, there is the L pragma. For
the rest, there is B.

  use Syntax::Construct qw( // ... /r );

  my $x = shift // 'default';
  my $y = $x =~ s/de(fault)/$1/r;
  if ($y =~ /^fault/) {
      ...
  }

There are two subroutines (not exported) which you can use to query
the lists of constructs programmatically: C and
C (see below).

  my @constructs = Syntax::Construct::introduced();
  say "$_ was introduced in ",
      Syntax::Construct::introduced($_) for @constructs;

=head1 DESCRIPTION

This module provides a simple way of specifying syntactic constructs
that are not implemented via the L pragma, but are still not
compatible with older versions of Perl.

It's the programmer's responsibility to track the constructs and list
them (but see L on how to extract the
information from existing code).

Using C doesn't really change
anything if you're running Perl 5.010+, but it gives much better error
messages in older versions:

  Unsupported construct //

instead of

  Search pattern not terminated

Three groups of people can benefit from the module:

=over 4

=item 1.

The authors of the module using L win, as they have
all the constructs in one place (i.e. L's
documentation) and they don't waste their time searching through
perldeltas and other places.

=item 2.

Users of their modules win as they get meaningful error messages
telling them which Perl version they need to upgrade to.

=item 3.

The programmer they hired to work around the problem wins as they know
what constructs to replace in the code to make it run in the ancient
version.

=back

=head2 Good Practice

Some programmers just use all the I their current Perl
version provides without any notice. This leads to weird error
messages in older Perl versions.

Some other programmers will place C towards the top of the
script, even if the only I they use is the C operator
available in 5.010 already. This prevents users of older versions of
Perl to run the script, even if it would otherwise be easily possible.

The kindest programmers will add C towards the top of
the script. But it means they have to remember or find out what
version introduced the I they use.

B liberates you from the need to remember all the
I together with Perl versions that introduced them. It
makes it easier for users of older Perl versions to migrate your code
to their system. And finally, it improves the error messages they get.

Similarly, it's a good practice to keep specifying C
postderef };> even if it's a no-op since 5.024: it makes your script
available for people running older Perl versions. The same applies to
C in 5.016 and later, etc.

=head1 EXPORT

Nothing. Using B with no parameters is an error,
giving it an empty list is a no-op (but you can then access the
C and C subroutines).

=over 4

=item introduced

Without arguments, returns a list of all the supported
constructs. With an argument, returns the version in which the given
construct was introduced.

=item removed

Same as C, but for removed constructs (e.g. auto-deref in
5.024).

=back

=head1 RECOGNISED CONSTRUCTS

=head2 5.008001

=head3 s-utf8-delimiters-hack

See L. The hack doesn't seem to work in 5.008
and older. Removed in 5.020.

=head2 5.010

=head3 recursive-sort

L.

=head3 //

L or L.

Alias: defined-or

=head3 ?PARNO

"Recursive Patterns" under L or
L.

Alias: regex-recursive-subpattern

=head3 ?<>

"Named Capture Buffers" under L or
LNAMEE<62>pattern)">.

Alias: regex-named-capture-group

=head3 ?|

Not mentioned in any Delta. See B<(?|pattern)> in L.

Alias: regex-reset-branch

=head3 quant+

"Possessive Quantifiers" under L or
L.

Aliases: regex-possessive-quantifier regex-possessive-match

=head3 regex-verbs

"Backtracking control verbs" under L
expressions> or L.


=head3 \K

"\K escape" under L or
L.

Alias: regex-keep-left

=head3 \R \v \h

Covers C<\V> and C<\H>, too. See "Vertical and horizontal whitespace,
and linebreak" under L or
L.

Aliases: \H \V regex-generic-linebreak regex-horizontal-whitespace regex-vertical-whitespace

=head3 \gN

"Relative backreferences" under L or
L.

Alias: regex-relative-backreference

=head3 readline()

L.

Alias: readline-argv

=head3 stack-file-test

L.

=head3 /p

C (preserve) modifier and C<${^PREMATCH}>, C<${^MATCH}> and
C<${^POSTMATCH}> variables. Not mentioned in any Delta. See
L.

Alias: regex-preserve-match-captures

=head3 lexical-$_

L. Removed in 5.024.

Alias: lexical-default-variable

=head3 pack<

See L

Alias: pack-byte-order-modifiers

=head2 5.012

=head3 package-version

L

=head3 ...

L or L

Aliases: yada-yada triple-dot statement-ellipsis

=head3 each-array

L

=head3 keys-array

L

=head3 values-array

L

=head3 delete-local

L

=head3 length-undef

See the ninth bullet in L
changes>.

=head3 \N

L.

Alias: regex-non-newline

=head3 while-readdir

C in a while-loop condition populates C<$_>. Not mentioned in
any delta, but see C in L.

=head2 5.014

=head3 ?^

L.

Alias: regex-use-default-modifiers

=head3 /r

L and L.

Aliases: non-destructive-subst non-destructive-substitution

=head3 /d

L and L.

Alias: regex-compile-as-default

=head3 /l

L and L.

Alias: regex-compile-as-locale

=head3 /u

L and L.

Aliases: regex-unicode-strings regex-compile-as-unicode-strings

=head3 /a

L and L.

Alias: regex-restrict-ascii-range

=head3 auto-deref

L
references>. See also C, C, C, C,
C, C, C, and C in L.
Removed in 5.024.

=head3 ^GLOBAL_PHASE

See B under
L.

Alias: global-phase

=head3 \o

L.

Alias: octal-escape

=head3 package-block

See B under L.

=head3 srand-return

See B under L.

=head3 prototype+

See L.

=head3 sig-warn-obj

See the second bullet in L.

=head2 5.016

=head3 charnames

See L.

=head3 __FILE__()

See L.

Aliases: __LINE__() __PACKAGE__()

=head2 5.018

=head3 computed-labels

L

=head3 while-each

See in L or C in L.

=head3 method-on-any-string

See [perl #105922] in L.

=head3 split-space

See L.

=head2 5.020

=head3 attr-prototype

L

Alias: attribute-prototype

=head3 drand48

L.
Note that on OpenBSD, Perl 5.020+ uses the system's own C
unless seeded.

=head3 %slice

L

Alias: hash-slice

=head3 unicode6.3

L

Alias: unicode-6.3

=head3 \p{Unicode}

See B in
L.

Alias: regex-property-unicode

=head3 utf8-locale

See B in
L.

=head3 s-utf8-delimiters

See L: in older Perl versions, a
hack around was possible: to specify the delimiter twice in
substitution. Use C if your code uses it.

Alias: wide-char-delimiters

=head2 5.022

=head3 <<>>

L

Aliases: double-diamond operator-double-diamond

=head3 \b{}

L

Aliases: regex-unicode-grapheme-cluster-boundary regex-unicode-boundary regex-unicode-word-boundary regex-unicode-sentence-boundary regex-unicode-line-break-boundary \b{sb} \b{wb} \b{gcb}

=head3 /n

L

Alias: regex-non-capturing

=head3 unicode7.0

See B in
L.

Alias: unicode-7.0

=head3 attr-const

L

Alias: attribute-const

=head3 fileno-dir

L

=head3 ()x=

L

Alias: list-repetition-assignment

=head3 hexfloat

L

Alias: hexadecimal-floating-numbers

=head3 chr-inf

L

Alias: pack-inf

=head3 empty-slice

L

=head3 /x-unicode

See B in
L.

Aliases: regex-x-unicode regex-x-handles-unicode

=head2 5.024

=head3 unicode8.0

L.

Alias: unicode-8.0

=head3 \b{lb}

L.

=head3 sprintf-reorder

L.

Aliases: printf-precision-argument-reorder sprintf-precision-argument-reorder

=head2 5.026

=head3 <<~

L.

Alias: heredoc-indent

=head3 /xx

L.

Alias: regex-xx

=head3 ^CAPTURE

See C<@{^CAPTURE}>, C<%{^CAPTURE}>, and C<%{^CAPTURE_ALL}> in
L.

Alias: capture-variable

=head3 unicode9.0

L.

Alias: unicode-9.0

=head3 unicode-scx

See I<"Use of \p{script} uses the improved Script_Extensions property">
in L.

=head3 scalar%

See L. Specifying this
construct means the 5.026+ behaviour, i.e. C returns the number
of keys.

Alias: scalar-hash

=head2 5.028

=head3 delete%

See L.

Alias: hash-delete-slice

=head3 unicode10.0

See L.

Alias: unicode-10.0

=head3 state@=

See L.

Aliases: state-array state-hash list-context-state

=head2 5.030

=head3 unicode12.1

L

Alias: unicode-12.1

=head3 uniprop_wildcards

L

=head3 qr'N

L

Alias: named-char-in-single-quoted-regex

=head3 turkic-casing

See L.
B the actual behaviour depends on the operating system's
locale support. E.g. FreeBSD, DragonFly, and Solaris are known not to
support it.

=head3 ^RE_COMPILE_RECURSION_LIMIT

Not mentioned in any Delta. See L.

Alias: re-compile-recursion-limit

=head2 5.032

=head3 unicode13.0

L

Alias: unicode-13.0

=head3 chained-comparisons

L

=head3 unicode-identifier-status

L

Alias: unicode-identifier-type

=head3 unicode-name-property

L

=head2 5.034

=head3 {,n}

L

Alias: empty-left-quantifier

=head3 0o

L

Alias: octal-literals

=head3 blanks-in-curlies

L

=head2 5.036

=head3 unicode14.0

L

=head2 5.038

=head3 unicode15.0

L

=head3 ^HOOK

L

Alias: keyword-hook

=head3 signature-default-operator

L

=head3 INCDIR

L

=head3 *{}

L

Alias: optimistic-eval

=head3 REG_INF_I32_MAX

L

=head3 ^LAST_SUCCESSFUL_PATTERN

L

=head2 5.040

=head3 ^^

L

Alias: logical-xor

=head3 __CLASS__

L.

=head3 :reader

L

=head2 5.042

=head3 :writer

L

=head3 my_method

L

=head3 ->&

L<< perl5420delta/Lexical method invocation operator ->& >>

Alias: lexical-method-invocation-operator

=head3 unicode16.0

L

=head3 ^^=

L

Alias: assign-logical-xor

=for completeness
=head2 old

=head2 Removed Constructs

Only constructs not mentioned above are listed here, i.e. constructs
that were introduced before 5.008001.

=head3 ??

Removed in 5.022. See L
explicit operator has been removed>.

=head3 no-sigil

Removed in 5.022, not documented. Before that, if the first argument
to C, C, C, C, C, C,
C, and C was a global variable, it was possible to omit
its sigil, e.g.

  push arr, 12;  # same as push @arr, 12

=head3 for-qw

Removed in 5.018. See L.

=head3 @_=split

Removed in 5.012, but documented in 5.014. See L.

Alias: split-populates-@_

=head2 Accepted Features

Some features have been accepted in Perl (C and
C in 5.024, C in 5.026). In the spirit of
Syntax::Construct, you should still declare them, even if their usage
has no effect in newer Perl versions to provide meaningful error
messages to users of older versions.

=head1 AUTHOR

E. Choroba, C<<  >>

=head2 Contributors

Gabor Szabo, JJ Merelo, tynovsky, Chris White, Mohammad S Anwar,
Branislav Zahradnik

=head1 BUGS

Please report any bugs or feature requests to the GitHub repository,
see below.

=head2 Unstable Perl Versions

In development versions of Perl, the removal of constructs is tested
against the coming stable version -- e.g., 5.023 forbids all the
removed constructs of 5.024. The behaviour of the module in such
circumstances might still be, um, unstable.

=head1 SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc Syntax::Construct

You can also look for information at:

=over 4

=item * GitHub Repository

L

Feel free to report issues and submit pull requests.

=item * MetaCPAN, Open Source Search Engine for CPAN

L

=item * Search CPAN

L

=back

=head1 SEE ALSO

L, L

=head1 LICENSE AND COPYRIGHT

Copyright 2013 - 2026 E. Choroba.

This program is free software; you can redistribute it and/or modify it
under the terms of the the Artistic License (2.0). You may obtain a
copy of the full license at:

L

Any use, modification, and distribution of the Standard or Modified
Versions is governed by this Artistic License. By using, modifying or
distributing the Package, you accept this license. Do not use, modify,
or distribute the Package, if you do not accept this license.

If your Modified Version has been derived from a Modified Version made
by someone other than you, you are nevertheless required to ensure that
your Modified Version complies with the requirements of this license.

This license does not grant you the right to use any trademark, service
mark, tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge
patent license to make, have made, use, offer to sell, sell, import and
otherwise transfer the Package with respect to any patent claims
licensable by the Copyright Holder that are necessarily infringed by the
Package. If you institute patent litigation (including a cross-claim or
counterclaim) against any party alleging that the Package constitutes
direct or contributory patent infringement, then this Artistic License
to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER
AND CONTRIBUTORS "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES.
THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY
YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR
CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE,
EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


=cut

__PACKAGE__