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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 = '2.08'; |
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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( ($fglob && *$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 | local $SIG{__DIE__}; |
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86 | eval "require $base"; |
87 | # Only ignore "Can't locate" errors from our eval require. |
88 | # Other fatal errors (syntax etc) must be reported. |
89 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
90 | unless (%{"$base\::"}) { |
91 | require Carp; |
92 | Carp::croak(<<ERROR); |
93 | Base class package "$base" is empty. |
94 | (Perhaps you need to 'use' the module which defines that package first.) |
95 | ERROR |
96 | |
97 | } |
98 | ${$base.'::VERSION'} = "-1, set by base.pm" |
99 | unless defined ${$base.'::VERSION'}; |
100 | } |
101 | push @{"$inheritor\::ISA"}, $base; |
102 | |
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103 | if ( has_fields($base) || has_attr($base) ) { |
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104 | # No multiple fields inheritance *suck* |
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105 | if ($fields_base) { |
106 | require Carp; |
107 | Carp::croak("Can't multiply inherit %FIELDS"); |
108 | } else { |
109 | $fields_base = $base; |
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110 | } |
111 | } |
112 | } |
113 | |
114 | if( defined $fields_base ) { |
115 | inherit_fields($inheritor, $fields_base); |
116 | } |
117 | } |
118 | |
119 | |
120 | sub inherit_fields { |
121 | my($derived, $base) = @_; |
122 | |
123 | return SUCCESS unless $base; |
124 | |
125 | my $battr = get_attr($base); |
126 | my $dattr = get_attr($derived); |
127 | my $dfields = get_fields($derived); |
128 | my $bfields = get_fields($base); |
129 | |
130 | $dattr->[0] = @$battr; |
131 | |
132 | if( keys %$dfields ) { |
133 | warn "$derived is inheriting from $base but already has its own ". |
134 | "fields!\n". |
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135 | "This will cause problems.\n". |
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136 | "Be sure you use base BEFORE declaring fields\n"; |
137 | } |
138 | |
139 | # Iterate through the base's fields adding all the non-private |
140 | # ones to the derived class. Hang on to the original attribute |
141 | # (Public, Private, etc...) and add Inherited. |
142 | # This is all too complicated to do efficiently with add_fields(). |
143 | while (my($k,$v) = each %$bfields) { |
144 | my $fno; |
145 | if ($fno = $dfields->{$k} and $fno != $v) { |
146 | require Carp; |
147 | Carp::croak ("Inherited %FIELDS can't override existing %FIELDS"); |
148 | } |
149 | |
150 | if( $battr->[$v] & PRIVATE ) { |
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151 | $dattr->[$v] = PRIVATE | INHERITED; |
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152 | } |
153 | else { |
154 | $dattr->[$v] = INHERITED | $battr->[$v]; |
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155 | $dfields->{$k} = $v; |
156 | } |
157 | } |
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158 | |
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159 | foreach my $idx (1..$#{$battr}) { |
160 | next if defined $dattr->[$idx]; |
161 | $dattr->[$idx] = $battr->[$idx] & INHERITED; |
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162 | } |
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163 | } |
164 | |
165 | |
166 | 1; |
167 | |
168 | __END__ |
169 | |
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170 | =head1 NAME |
171 | |
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172 | base - Establish IS-A relationship with base classes at compile time |
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173 | |
174 | =head1 SYNOPSIS |
175 | |
176 | package Baz; |
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177 | use base qw(Foo Bar); |
178 | |
179 | =head1 DESCRIPTION |
180 | |
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181 | Allows you to both load one or more modules, while setting up inheritance from |
182 | those modules at the same time. Roughly similar in effect to |
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183 | |
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184 | package Baz; |
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185 | BEGIN { |
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186 | require Foo; |
187 | require Bar; |
188 | push @ISA, qw(Foo Bar); |
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189 | } |
190 | |
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191 | If any of the listed modules are not loaded yet, I<base> silently attempts to |
192 | C<require> them (and silently continues if the C<require> failed). Whether to |
193 | C<require> a base class module is determined by the absence of a global variable |
194 | $VERSION in the base package. If $VERSION is not detected even after loading |
195 | it, <base> will define $VERSION in the base package, setting it to the string |
196 | C<-1, set by base.pm>. |
197 | |
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198 | Will also initialize the fields if one of the base classes has it. |
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199 | Multiple inheritance of fields is B<NOT> supported, if two or more |
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200 | base classes each have inheritable fields the 'base' pragma will |
201 | croak. See L<fields>, L<public> and L<protected> for a description of |
202 | this feature. |
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203 | |
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204 | =head1 DIAGNOSTICS |
205 | |
206 | =over 4 |
207 | |
208 | =item Base class package "%s" is empty. |
209 | |
210 | base.pm was unable to require the base package, because it was not |
211 | found in your path. |
212 | |
213 | =back |
214 | |
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215 | =head1 HISTORY |
216 | |
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217 | This module was introduced with Perl 5.004_04. |
218 | |
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219 | Attempting to inherit from yourself generates a warning: |
220 | |
221 | use Foo; |
222 | use base 'Foo'; |
223 | |
224 | # Class 'Foo' tried to inherit from itself |
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225 | |
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226 | =head1 CAVEATS |
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227 | |
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228 | Due to the limitations of the implementation, you must use |
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229 | base I<before> you declare any of your own fields. |
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230 | |
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231 | |
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232 | =head1 SEE ALSO |
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233 | |
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234 | L<fields> |
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235 | |
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236 | =cut |