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1 | =head1 NAME |
2 | |
3 | base - Establish IS-A relationship with base class at compile time |
4 | |
5 | =head1 SYNOPSIS |
6 | |
7 | package Baz; |
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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 | |
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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 has 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 | |
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28 | This module was introduced with Perl 5.004_04. |
29 | |
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30 | =head1 SEE ALSO |
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31 | |
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32 | L<fields> |
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33 | |
34 | =cut |
35 | |
36 | package base; |
37 | |
38 | sub import { |
39 | my $class = shift; |
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40 | my $fields_base; |
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41 | |
42 | foreach my $base (@_) { |
43 | unless (defined %{"$base\::"}) { |
44 | eval "require $base"; |
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45 | # Only ignore "Can't locate" errors from our eval require. |
46 | # Other fatal errors (syntax etc) must be reported. |
47 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
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48 | unless (defined %{"$base\::"}) { |
49 | require Carp; |
50 | Carp::croak("Base class package \"$base\" is empty.\n", |
51 | "\t(Perhaps you need to 'use' the module ", |
52 | "which defines that package first.)"); |
53 | } |
54 | } |
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55 | |
56 | # A simple test like (defined %{"$base\::FIELDS"}) will |
57 | # sometimes produce typo warnings because it would create |
58 | # the hash if it was not present before. |
59 | my $fglob; |
60 | if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) { |
61 | if ($fields_base) { |
62 | require Carp; |
63 | Carp::croak("Can't multiply inherit %FIELDS"); |
64 | } else { |
65 | $fields_base = $base; |
66 | } |
67 | } |
68 | } |
69 | my $pkg = caller(0); |
70 | push @{"$pkg\::ISA"}, @_; |
71 | if ($fields_base) { |
72 | require fields; |
73 | fields::inherit($pkg, $fields_base); |
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74 | } |
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75 | } |
76 | |
77 | 1; |