| 1 | package UNIVERSAL; |
| 2 | |
| 3 | # UNIVERSAL should not contain any extra subs/methods beyond those |
| 4 | # that it exists to define. The use of Exporter below is a historical |
| 5 | # accident that should be fixed sometime. |
| 6 | require Exporter; |
| 7 | *import = \&Exporter::import; |
| 8 | @EXPORT_OK = qw(isa can); |
| 9 | |
| 10 | 1; |
| 11 | __END__ |
| 12 | |
| 13 | =head1 NAME |
| 14 | |
| 15 | UNIVERSAL - base class for ALL classes (blessed references) |
| 16 | |
| 17 | =head1 SYNOPSIS |
| 18 | |
| 19 | $io = $fd->isa("IO::Handle"); |
| 20 | $sub = $obj->can('print'); |
| 21 | |
| 22 | $yes = UNIVERSAL::isa($ref, "HASH"); |
| 23 | |
| 24 | =head1 DESCRIPTION |
| 25 | |
| 26 | C<UNIVERSAL> is the base class which all bless references will inherit from, |
| 27 | see L<perlobj> |
| 28 | |
| 29 | C<UNIVERSAL> provides the following methods |
| 30 | |
| 31 | =over 4 |
| 32 | |
| 33 | =item isa ( TYPE ) |
| 34 | |
| 35 | C<isa> returns I<true> if C<REF> is blessed into package C<TYPE> |
| 36 | or inherits from package C<TYPE>. |
| 37 | |
| 38 | C<isa> can be called as either a static or object method call. |
| 39 | |
| 40 | =item can ( METHOD ) |
| 41 | |
| 42 | C<can> checks if the object has a method called C<METHOD>. If it does |
| 43 | then a reference to the sub is returned. If it does not then I<undef> |
| 44 | is returned. |
| 45 | |
| 46 | C<can> can be called as either a static or object method call. |
| 47 | |
| 48 | =item VERSION ( [ REQUIRE ] ) |
| 49 | |
| 50 | C<VERSION> will return the value of the variable C<$VERSION> in the |
| 51 | package the object is blessed into. If C<REQUIRE> is given then |
| 52 | it will do a comparison and die if the package version is not |
| 53 | greater than or equal to C<REQUIRE>. |
| 54 | |
| 55 | C<VERSION> can be called as either a static or object method call. |
| 56 | |
| 57 | =back |
| 58 | |
| 59 | The C<isa> and C<can> methods can also be called as subroutines |
| 60 | |
| 61 | =over 4 |
| 62 | |
| 63 | =item UNIVERSAL::isa ( VAL, TYPE ) |
| 64 | |
| 65 | C<isa> returns I<true> if the first argument is a reference and either |
| 66 | of the following statements is true. |
| 67 | |
| 68 | =over 8 |
| 69 | |
| 70 | =item |
| 71 | |
| 72 | C<VAL> is a blessed reference and is blessed into package C<TYPE> |
| 73 | or inherits from package C<TYPE> |
| 74 | |
| 75 | =item |
| 76 | |
| 77 | C<VAL> is a reference to a C<TYPE> of perl variable (er 'HASH') |
| 78 | |
| 79 | =back |
| 80 | |
| 81 | =item UNIVERSAL::can ( VAL, METHOD ) |
| 82 | |
| 83 | If C<VAL> is a blessed reference which has a method called C<METHOD>, |
| 84 | C<can> returns a reference to the subroutine. If C<VAL> is not |
| 85 | a blessed reference, or if it does not have a method C<METHOD>, |
| 86 | I<undef> is returned. |
| 87 | |
| 88 | =back |
| 89 | |
| 90 | These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>. |
| 91 | If you want simple local access to them you can do |
| 92 | |
| 93 | *isa = \&UNIVERSAL::isa; |
| 94 | |
| 95 | to import isa into your package. |
| 96 | |
| 97 | =cut |