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