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86530b38 AT |
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, set 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 5.006_001; | |
48 | our $VERSION = "1.03"; | |
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 | my $vglob; | |
58 | if ($vglob = ${"$base\::"}{VERSION} and *$vglob{SCALAR}) { | |
59 | $$vglob = "-1, set by base.pm" unless defined $$vglob; | |
60 | } else { | |
61 | eval "require $base"; | |
62 | # Only ignore "Can't locate" errors from our eval require. | |
63 | # Other fatal errors (syntax etc) must be reported. | |
64 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; | |
65 | unless (%{"$base\::"}) { | |
66 | require Carp; | |
67 | Carp::croak("Base class package \"$base\" is empty.\n", | |
68 | "\t(Perhaps you need to 'use' the module ", | |
69 | "which defines that package first.)"); | |
70 | } | |
71 | ${"$base\::VERSION"} = "-1, set by base.pm" unless defined ${"$base\::VERSION"}; | |
72 | } | |
73 | push @{"$pkg\::ISA"}, $base; | |
74 | ||
75 | # A simple test like (defined %{"$base\::FIELDS"}) will | |
76 | # sometimes produce typo warnings because it would create | |
77 | # the hash if it was not present before. | |
78 | my $fglob; | |
79 | if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) { | |
80 | if ($fields_base) { | |
81 | require Carp; | |
82 | Carp::croak("Can't multiply inherit %FIELDS"); | |
83 | } else { | |
84 | $fields_base = $base; | |
85 | } | |
86 | } | |
87 | } | |
88 | if ($fields_base) { | |
89 | require fields; | |
90 | fields::inherit($pkg, $fields_base); | |
91 | } | |
92 | } | |
93 | ||
94 | 1; |