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1 | # Scalar::Util.pm |
| 2 | # |
| 3 | # Copyright (c) 1997-2000 Graham Barr <gbarr@pobox.com>. All rights reserved. |
| 4 | # This program is free software; you can redistribute it and/or |
| 5 | # modify it under the same terms as Perl itself. |
| 6 | |
| 7 | package Scalar::Util; |
| 8 | |
| 9 | require Exporter; |
| 10 | require List::Util; # List::Util loads the XS |
| 11 | |
| 12 | $VERSION = $VERSION = $List::Util::VERSION; |
| 13 | @ISA = qw(Exporter); |
| 14 | @EXPORT_OK = qw(blessed dualvar reftype weaken isweak tainted readonly); |
| 15 | |
| 16 | sub export_fail { |
| 17 | if (grep { /^(weaken|isweak)$/ } @_ ) { |
| 18 | require Carp; |
| 19 | Carp::croak("Weak references are not implemented in the version of perl"); |
| 20 | } |
| 21 | if (grep { /^dualvar$/ } @_ ) { |
| 22 | require Carp; |
| 23 | Carp::croak("dualvar is only avaliable with the XS version"); |
| 24 | } |
| 25 | |
| 26 | @_; |
| 27 | } |
| 28 | |
| f4a2945e |
29 | 1; |
| 30 | |
| 31 | __END__ |
| 32 | |
| 33 | =head1 NAME |
| 34 | |
| 35 | Scalar::Util - A selection of general-utility scalar subroutines |
| 36 | |
| 37 | =head1 SYNOPSIS |
| 38 | |
| 39 | use Scalar::Util qw(blessed dualvar reftype weaken isweak); |
| 40 | |
| 41 | =head1 DESCRIPTION |
| 42 | |
| 43 | C<Scalar::Util> contains a selection of subroutines that people have |
| 44 | expressed would be nice to have in the perl core, but the usage would |
| 45 | not really be high enough to warrant the use of a keyword, and the size |
| 46 | so small such that being individual extensions would be wasteful. |
| 47 | |
| 48 | By default C<Scalar::Util> does not export any subroutines. The |
| 49 | subroutines defined are |
| 50 | |
| 51 | =over 4 |
| 52 | |
| 53 | =item blessed EXPR |
| 54 | |
| 55 | If EXPR evaluates to a blessed reference the name of the package |
| 56 | that it is blessed into is returned. Otherwise C<undef> is returned. |
| 57 | |
| 58 | =item dualvar NUM, STRING |
| 59 | |
| 60 | Returns a scalar that has the value NUM in a numeric context and the |
| 61 | value STRING in a string context. |
| 62 | |
| 63 | $foo = dualvar 10, "Hello"; |
| 64 | $num = $foo + 2; # 12 |
| 65 | $str = $foo . " world"; # Hello world |
| 66 | |
| 67 | =item isweak EXPR |
| 68 | |
| 69 | If EXPR is a scalar which is a weak reference the result is true. |
| 70 | |
| 71 | =item reftype EXPR |
| 72 | |
| 73 | If EXPR evaluates to a reference the type of the variable referenced |
| 74 | is returned. Otherwise C<undef> is returned. |
| 75 | |
| 76 | =item weaken REF |
| 77 | |
| 78 | REF will be turned into a weak reference. This means that it will not |
| 79 | hold a reference count on the object it references. Also when the reference |
| 80 | count on that object reaches zero, REF will be set to undef. |
| 81 | |
| 82 | This is useful for keeping copies of references , but you don't want to |
| 83 | prevent the object being DESTROY-ed at it's usual time. |
| 84 | |
| 85 | =back |
| 86 | |
| 87 | =head1 COPYRIGHT |
| 88 | |
| 89 | Copyright (c) 1997-2000 Graham Barr <gbarr@pobox.com>. All rights reserved. |
| 90 | This program is free software; you can redistribute it and/or modify it |
| 91 | under the same terms as Perl itself. |
| 92 | |
| 93 | except weaken and isweak which are |
| 94 | |
| 95 | Copyright (c) 1999 Tuomas J. Lukka <lukka@iki.fi>. All rights reserved. |
| 96 | This program is free software; you can redistribute it and/or modify it |
| 97 | under the same terms as perl itself. |
| 98 | |
| 99 | =head1 BLATANT PLUG |
| 100 | |
| 101 | The weaken and isweak subroutines in this module and the patch to the core Perl |
| 102 | were written in connection with the APress book `Tuomas J. Lukka's Definitive |
| 103 | Guide to Object-Oriented Programming in Perl', to avoid explaining why certain |
| 104 | things would have to be done in cumbersome ways. |
| 105 | |
| 106 | =cut |
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