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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' |
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22 | pragma will croak if multiple base classes have a %FIELDS hash. See |
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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 | 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 |
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33 | C<-1, set by base.pm>. |
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34 | |
35 | =head1 HISTORY |
36 | |
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37 | This module was introduced with Perl 5.004_04. |
38 | |
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39 | =head1 SEE ALSO |
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40 | |
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41 | L<fields> |
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42 | |
43 | =cut |
44 | |
45 | package base; |
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46 | |
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47 | use 5.006_001; |
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48 | our $VERSION = "1.02"; |
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49 | |
50 | sub import { |
51 | my $class = shift; |
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52 | my $fields_base; |
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53 | my $pkg = caller(0); |
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54 | |
55 | foreach my $base (@_) { |
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56 | next if $pkg->isa($base); |
57 | push @{"$pkg\::ISA"}, $base; |
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58 | my $vglob; |
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59 | unless (${*{"$base\::VERSION"}{SCALAR}}) { |
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60 | eval "require $base"; |
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61 | # Only ignore "Can't locate" errors from our eval require. |
62 | # Other fatal errors (syntax etc) must be reported. |
63 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
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64 | unless (%{"$base\::"}) { |
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65 | require Carp; |
66 | Carp::croak("Base class package \"$base\" is empty.\n", |
67 | "\t(Perhaps you need to 'use' the module ", |
68 | "which defines that package first.)"); |
69 | } |
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70 | ${"$base\::VERSION"} = "-1, set by base.pm" |
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71 | unless ${*{"$base\::VERSION"}{SCALAR}}; |
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72 | } |
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73 | |
74 | # A simple test like (defined %{"$base\::FIELDS"}) will |
75 | # sometimes produce typo warnings because it would create |
76 | # the hash if it was not present before. |
77 | my $fglob; |
78 | if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) { |
79 | if ($fields_base) { |
80 | require Carp; |
81 | Carp::croak("Can't multiply inherit %FIELDS"); |
82 | } else { |
83 | $fields_base = $base; |
84 | } |
85 | } |
86 | } |
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87 | if ($fields_base) { |
88 | require fields; |
89 | fields::inherit($pkg, $fields_base); |
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90 | } |
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91 | } |
92 | |
93 | 1; |