Commit | Line | Data |
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fb73857a | 1 | =head1 NAME |
2 | ||
3 | base - Establish IS-A relationship with base class at compile time | |
4 | ||
5 | =head1 SYNOPSIS | |
6 | ||
7 | package Baz; | |
fb73857a | 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 | ||
f1192cee GA |
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' | |
b8bc843f | 22 | pragma will croak if multiple base classes have a %FIELDS hash. See |
f1192cee GA |
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 | ||
b8bc843f A |
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 | ||
fb73857a | 37 | This module was introduced with Perl 5.004_04. |
38 | ||
f1192cee | 39 | =head1 SEE ALSO |
fb73857a | 40 | |
f1192cee | 41 | L<fields> |
fb73857a | 42 | |
43 | =cut | |
44 | ||
45 | package base; | |
17f410f9 GS |
46 | |
47 | use 5.005_64; | |
48 | our $VERSION = "1.01"; | |
fb73857a | 49 | |
50 | sub import { | |
51 | my $class = shift; | |
f1192cee | 52 | my $fields_base; |
f30a1143 | 53 | my $pkg = caller(0); |
fb73857a | 54 | |
55 | foreach my $base (@_) { | |
f30a1143 JT |
56 | next if $pkg->isa($base); |
57 | push @{"$pkg\::ISA"}, $base; | |
b8bc843f | 58 | unless (exists ${"$base\::"}{VERSION}) { |
fb73857a | 59 | eval "require $base"; |
9b599b2a GS |
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 /; | |
c5be433b | 63 | unless (%{"$base\::"}) { |
fb73857a | 64 | require Carp; |
65 | Carp::croak("Base class package \"$base\" is empty.\n", | |
66 | "\t(Perhaps you need to 'use' the module ", | |
67 | "which defines that package first.)"); | |
68 | } | |
b8bc843f A |
69 | ${"$base\::VERSION"} = "-1, set by base.pm" |
70 | unless exists ${"$base\::"}{VERSION}; | |
fb73857a | 71 | } |
f1192cee GA |
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 = $base; | |
83 | } | |
84 | } | |
85 | } | |
f1192cee GA |
86 | if ($fields_base) { |
87 | require fields; | |
88 | fields::inherit($pkg, $fields_base); | |
fb73857a | 89 | } |
fb73857a | 90 | } |
91 | ||
92 | 1; |