| 1 | =head1 NAME |
| 2 | |
| 3 | base - Establish IS-A relationship with base class at compile time |
| 4 | |
| 5 | =head1 SYNOPSIS |
| 6 | |
| 7 | package Baz; |
| 8 | use base qw(Foo Bar); |
| 9 | |
| 10 | =head1 DESCRIPTION |
| 11 | |
| 12 | Roughly similar in effect to |
| 13 | |
| 14 | BEGIN { |
| 15 | require Foo; |
| 16 | require Bar; |
| 17 | push @ISA, qw(Foo Bar); |
| 18 | } |
| 19 | |
| 20 | Will also initialize the %FIELDS hash if one of the base classes has |
| 21 | it. Multiple inheritance of %FIELDS is not supported. The 'base' |
| 22 | pragma will croak if multiple base classes have a %FIELDS hash. See |
| 23 | L<fields> for a description of this feature. |
| 24 | |
| 25 | When strict 'vars' is in scope I<base> also let you assign to @ISA |
| 26 | without having to declare @ISA with the 'vars' pragma first. |
| 27 | |
| 28 | If any of the base classes are not loaded yet, I<base> silently |
| 29 | C<require>s them. Whether to C<require> a base class package is |
| 30 | determined by the absence of a global $VERSION in the base package. |
| 31 | If $VERSION is not detected even after loading it, <base> will |
| 32 | define $VERSION in the base package, setting it to the string |
| 33 | C<-1, defined by base.pm>. |
| 34 | |
| 35 | =head1 HISTORY |
| 36 | |
| 37 | This module was introduced with Perl 5.004_04. |
| 38 | |
| 39 | =head1 SEE ALSO |
| 40 | |
| 41 | L<fields> |
| 42 | |
| 43 | =cut |
| 44 | |
| 45 | package base; |
| 46 | |
| 47 | use 5.005_64; |
| 48 | our $VERSION = "1.01"; |
| 49 | |
| 50 | sub import { |
| 51 | my $class = shift; |
| 52 | my $fields_base; |
| 53 | my $pkg = caller(0); |
| 54 | |
| 55 | foreach my $base (@_) { |
| 56 | next if $pkg->isa($base); |
| 57 | push @{"$pkg\::ISA"}, $base; |
| 58 | unless (exists ${"$base\::"}{VERSION}) { |
| 59 | eval "require $base"; |
| 60 | # Only ignore "Can't locate" errors from our eval require. |
| 61 | # Other fatal errors (syntax etc) must be reported. |
| 62 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
| 63 | unless (%{"$base\::"}) { |
| 64 | require Carp; |
| 65 | Carp::croak("Base class package \"$base\" is empty.\n", |
| 66 | "\t(Perhaps you need to 'use' the module ", |
| 67 | "which defines that package first.)"); |
| 68 | } |
| 69 | ${"$base\::VERSION"} = "-1, set by base.pm" |
| 70 | unless exists ${"$base\::"}{VERSION}; |
| 71 | } |
| 72 | |
| 73 | # A simple test like (defined %{"$base\::FIELDS"}) will |
| 74 | # sometimes produce typo warnings because it would create |
| 75 | # the hash if it was not present before. |
| 76 | my $fglob; |
| 77 | if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) { |
| 78 | if ($fields_base) { |
| 79 | require Carp; |
| 80 | Carp::croak("Can't multiply inherit %FIELDS"); |
| 81 | } else { |
| 82 | $fields_base = $base; |
| 83 | } |
| 84 | } |
| 85 | } |
| 86 | if ($fields_base) { |
| 87 | require fields; |
| 88 | fields::inherit($pkg, $fields_base); |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | 1; |