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1 | package base; |
2 | |
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3 | use strict 'vars'; |
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4 | use vars qw($VERSION); |
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5 | $VERSION = '2.10'; |
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6 | |
7 | # constant.pm is slow |
8 | sub SUCCESS () { 1 } |
9 | |
10 | sub PUBLIC () { 2**0 } |
11 | sub PRIVATE () { 2**1 } |
12 | sub INHERITED () { 2**2 } |
13 | sub PROTECTED () { 2**3 } |
14 | |
15 | |
16 | my $Fattr = \%fields::attr; |
17 | |
18 | sub has_fields { |
19 | my($base) = shift; |
20 | my $fglob = ${"$base\::"}{FIELDS}; |
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21 | return( ($fglob && 'GLOB' eq ref($fglob) && *$fglob{HASH}) ? 1 : 0 ); |
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22 | } |
23 | |
24 | sub has_version { |
25 | my($base) = shift; |
26 | my $vglob = ${$base.'::'}{VERSION}; |
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27 | return( ($vglob && *$vglob{SCALAR}) ? 1 : 0 ); |
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28 | } |
29 | |
30 | sub has_attr { |
31 | my($proto) = shift; |
32 | my($class) = ref $proto || $proto; |
33 | return exists $Fattr->{$class}; |
34 | } |
35 | |
36 | sub get_attr { |
37 | $Fattr->{$_[0]} = [1] unless $Fattr->{$_[0]}; |
38 | return $Fattr->{$_[0]}; |
39 | } |
40 | |
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41 | if ($] < 5.009) { |
42 | *get_fields = sub { |
43 | # Shut up a possible typo warning. |
44 | () = \%{$_[0].'::FIELDS'}; |
45 | my $f = \%{$_[0].'::FIELDS'}; |
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46 | |
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47 | # should be centralized in fields? perhaps |
48 | # fields::mk_FIELDS_be_OK. Peh. As long as %{ $package . '::FIELDS' } |
49 | # is used here anyway, it doesn't matter. |
50 | bless $f, 'pseudohash' if (ref($f) ne 'pseudohash'); |
51 | |
52 | return $f; |
53 | } |
54 | } |
55 | else { |
56 | *get_fields = sub { |
57 | # Shut up a possible typo warning. |
58 | () = \%{$_[0].'::FIELDS'}; |
59 | return \%{$_[0].'::FIELDS'}; |
60 | } |
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61 | } |
62 | |
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63 | sub import { |
64 | my $class = shift; |
65 | |
66 | return SUCCESS unless @_; |
67 | |
68 | # List of base classes from which we will inherit %FIELDS. |
69 | my $fields_base; |
70 | |
71 | my $inheritor = caller(0); |
72 | |
73 | foreach my $base (@_) { |
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74 | if ( $inheritor eq $base ) { |
75 | warn "Class '$inheritor' tried to inherit from itself\n"; |
76 | } |
77 | |
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78 | next if $inheritor->isa($base); |
79 | |
80 | if (has_version($base)) { |
81 | ${$base.'::VERSION'} = '-1, set by base.pm' |
82 | unless defined ${$base.'::VERSION'}; |
83 | } |
84 | else { |
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85 | my $sigdie; |
86 | { |
87 | local $SIG{__DIE__}; |
88 | eval "require $base"; |
89 | # Only ignore "Can't locate" errors from our eval require. |
90 | # Other fatal errors (syntax etc) must be reported. |
91 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
92 | unless (%{"$base\::"}) { |
93 | require Carp; |
94 | Carp::croak(<<ERROR); |
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95 | Base class package "$base" is empty. |
96 | (Perhaps you need to 'use' the module which defines that package first.) |
97 | ERROR |
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98 | } |
99 | $sigdie = $SIG{__DIE__}; |
100 | } |
101 | # Make sure a global $SIG{__DIE__} makes it out of the localization. |
102 | $SIG{__DIE__} = $sigdie if defined $sigdie; |
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103 | ${$base.'::VERSION'} = "-1, set by base.pm" |
104 | unless defined ${$base.'::VERSION'}; |
105 | } |
106 | push @{"$inheritor\::ISA"}, $base; |
107 | |
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108 | if ( has_fields($base) || has_attr($base) ) { |
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109 | # No multiple fields inheritance *suck* |
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110 | if ($fields_base) { |
111 | require Carp; |
112 | Carp::croak("Can't multiply inherit %FIELDS"); |
113 | } else { |
114 | $fields_base = $base; |
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115 | } |
116 | } |
117 | } |
118 | |
119 | if( defined $fields_base ) { |
120 | inherit_fields($inheritor, $fields_base); |
121 | } |
122 | } |
123 | |
124 | |
125 | sub inherit_fields { |
126 | my($derived, $base) = @_; |
127 | |
128 | return SUCCESS unless $base; |
129 | |
130 | my $battr = get_attr($base); |
131 | my $dattr = get_attr($derived); |
132 | my $dfields = get_fields($derived); |
133 | my $bfields = get_fields($base); |
134 | |
135 | $dattr->[0] = @$battr; |
136 | |
137 | if( keys %$dfields ) { |
138 | warn "$derived is inheriting from $base but already has its own ". |
139 | "fields!\n". |
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140 | "This will cause problems.\n". |
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141 | "Be sure you use base BEFORE declaring fields\n"; |
142 | } |
143 | |
144 | # Iterate through the base's fields adding all the non-private |
145 | # ones to the derived class. Hang on to the original attribute |
146 | # (Public, Private, etc...) and add Inherited. |
147 | # This is all too complicated to do efficiently with add_fields(). |
148 | while (my($k,$v) = each %$bfields) { |
149 | my $fno; |
150 | if ($fno = $dfields->{$k} and $fno != $v) { |
151 | require Carp; |
152 | Carp::croak ("Inherited %FIELDS can't override existing %FIELDS"); |
153 | } |
154 | |
155 | if( $battr->[$v] & PRIVATE ) { |
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156 | $dattr->[$v] = PRIVATE | INHERITED; |
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157 | } |
158 | else { |
159 | $dattr->[$v] = INHERITED | $battr->[$v]; |
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160 | $dfields->{$k} = $v; |
161 | } |
162 | } |
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163 | |
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164 | foreach my $idx (1..$#{$battr}) { |
165 | next if defined $dattr->[$idx]; |
166 | $dattr->[$idx] = $battr->[$idx] & INHERITED; |
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167 | } |
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168 | } |
169 | |
170 | |
171 | 1; |
172 | |
173 | __END__ |
174 | |
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175 | =head1 NAME |
176 | |
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177 | base - Establish IS-A relationship with base classes at compile time |
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178 | |
179 | =head1 SYNOPSIS |
180 | |
181 | package Baz; |
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182 | use base qw(Foo Bar); |
183 | |
184 | =head1 DESCRIPTION |
185 | |
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186 | Allows you to both load one or more modules, while setting up inheritance from |
187 | those modules at the same time. Roughly similar in effect to |
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188 | |
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189 | package Baz; |
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190 | BEGIN { |
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191 | require Foo; |
192 | require Bar; |
193 | push @ISA, qw(Foo Bar); |
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194 | } |
195 | |
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196 | If any of the listed modules are not loaded yet, I<base> silently attempts to |
197 | C<require> them (and silently continues if the C<require> failed). Whether to |
198 | C<require> a base class module is determined by the absence of a global variable |
199 | $VERSION in the base package. If $VERSION is not detected even after loading |
200 | it, <base> will define $VERSION in the base package, setting it to the string |
201 | C<-1, set by base.pm>. |
202 | |
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203 | Will also initialize the fields if one of the base classes has it. |
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204 | Multiple inheritance of fields is B<NOT> supported, if two or more |
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205 | base classes each have inheritable fields the 'base' pragma will |
206 | croak. See L<fields>, L<public> and L<protected> for a description of |
207 | this feature. |
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208 | |
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209 | =head1 DIAGNOSTICS |
210 | |
211 | =over 4 |
212 | |
213 | =item Base class package "%s" is empty. |
214 | |
215 | base.pm was unable to require the base package, because it was not |
216 | found in your path. |
217 | |
218 | =back |
219 | |
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220 | =head1 HISTORY |
221 | |
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222 | This module was introduced with Perl 5.004_04. |
223 | |
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224 | Attempting to inherit from yourself generates a warning: |
225 | |
226 | use Foo; |
227 | use base 'Foo'; |
228 | |
229 | # Class 'Foo' tried to inherit from itself |
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230 | |
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231 | =head1 CAVEATS |
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232 | |
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233 | Due to the limitations of the implementation, you must use |
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234 | base I<before> you declare any of your own fields. |
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235 | |
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236 | |
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237 | =head1 SEE ALSO |
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238 | |
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239 | L<fields> |
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240 | |
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241 | =cut |