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[perl5.git] / lib / base.pm
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1package base;
2
864f8ab4 3use strict 'vars';
dc6d0c4f 4use vars qw($VERSION);
864f8ab4 5$VERSION = '2.03';
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6
7# constant.pm is slow
8sub SUCCESS () { 1 }
9
10sub PUBLIC () { 2**0 }
11sub PRIVATE () { 2**1 }
12sub INHERITED () { 2**2 }
13sub PROTECTED () { 2**3 }
14
15
16my $Fattr = \%fields::attr;
17
18sub has_fields {
19 my($base) = shift;
20 my $fglob = ${"$base\::"}{FIELDS};
864f8ab4 21 return( ($fglob && *$fglob{HASH}) ? 1 : 0 );
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22}
23
24sub has_version {
25 my($base) = shift;
26 my $vglob = ${$base.'::'}{VERSION};
864f8ab4 27 return( ($vglob && *$vglob{SCALAR}) ? 1 : 0 );
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28}
29
30sub has_attr {
31 my($proto) = shift;
32 my($class) = ref $proto || $proto;
33 return exists $Fattr->{$class};
34}
35
36sub get_attr {
37 $Fattr->{$_[0]} = [1] unless $Fattr->{$_[0]};
38 return $Fattr->{$_[0]};
39}
40
41sub get_fields {
42 # Shut up a possible typo warning.
43 () = \%{$_[0].'::FIELDS'};
44
45 return \%{$_[0].'::FIELDS'};
46}
47
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48sub import {
49 my $class = shift;
50
51 return SUCCESS unless @_;
52
53 # List of base classes from which we will inherit %FIELDS.
54 my $fields_base;
55
56 my $inheritor = caller(0);
57
58 foreach my $base (@_) {
59 next if $inheritor->isa($base);
60
61 if (has_version($base)) {
62 ${$base.'::VERSION'} = '-1, set by base.pm'
63 unless defined ${$base.'::VERSION'};
64 }
65 else {
66 local $SIG{__DIE__} = 'IGNORE';
67 eval "require $base";
68 # Only ignore "Can't locate" errors from our eval require.
69 # Other fatal errors (syntax etc) must be reported.
70 die if $@ && $@ !~ /^Can't locate .*? at \(eval /;
71 unless (%{"$base\::"}) {
72 require Carp;
73 Carp::croak(<<ERROR);
74Base class package "$base" is empty.
75 (Perhaps you need to 'use' the module which defines that package first.)
76ERROR
77
78 }
79 ${$base.'::VERSION'} = "-1, set by base.pm"
80 unless defined ${$base.'::VERSION'};
81 }
82 push @{"$inheritor\::ISA"}, $base;
83
dc6d0c4f 84 if ( has_fields($base) || has_attr($base) ) {
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85 # No multiple fields inheritence *suck*
86 if ($fields_base) {
87 require Carp;
88 Carp::croak("Can't multiply inherit %FIELDS");
89 } else {
90 $fields_base = $base;
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91 }
92 }
93 }
94
95 if( defined $fields_base ) {
96 inherit_fields($inheritor, $fields_base);
97 }
98}
99
100
101sub inherit_fields {
102 my($derived, $base) = @_;
103
104 return SUCCESS unless $base;
105
106 my $battr = get_attr($base);
107 my $dattr = get_attr($derived);
108 my $dfields = get_fields($derived);
109 my $bfields = get_fields($base);
110
111 $dattr->[0] = @$battr;
112
113 if( keys %$dfields ) {
114 warn "$derived is inheriting from $base but already has its own ".
115 "fields!\n".
116 "This will cause problems with pseudo-hashes.\n".
117 "Be sure you use base BEFORE declaring fields\n";
118 }
119
120 # Iterate through the base's fields adding all the non-private
121 # ones to the derived class. Hang on to the original attribute
122 # (Public, Private, etc...) and add Inherited.
123 # This is all too complicated to do efficiently with add_fields().
124 while (my($k,$v) = each %$bfields) {
125 my $fno;
126 if ($fno = $dfields->{$k} and $fno != $v) {
127 require Carp;
128 Carp::croak ("Inherited %FIELDS can't override existing %FIELDS");
129 }
130
131 if( $battr->[$v] & PRIVATE ) {
864f8ab4 132 $dattr->[$v] = PRIVATE | INHERITED;
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133 }
134 else {
135 $dattr->[$v] = INHERITED | $battr->[$v];
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136 $dfields->{$k} = $v;
137 }
138 }
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139
140 unless( keys %$bfields ) {
141 foreach my $idx (1..$#{$battr}) {
142 $dattr->[$idx] = $battr->[$idx] & INHERITED;
143 }
144 }
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145}
146
147
1481;
149
150__END__
151
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152=head1 NAME
153
154base - Establish IS-A relationship with base class at compile time
155
156=head1 SYNOPSIS
157
158 package Baz;
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159 use base qw(Foo Bar);
160
161=head1 DESCRIPTION
162
163Roughly similar in effect to
164
165 BEGIN {
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166 require Foo;
167 require Bar;
168 push @ISA, qw(Foo Bar);
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169 }
170
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171Will also initialize the fields if one of the base classes has it.
172Multiple Inheritence of fields is B<NOT> supported, if two or more
173base classes each have inheritable fields the 'base' pragma will
174croak. See L<fields>, L<public> and L<protected> for a description of
175this feature.
f1192cee 176
bcbfb61f 177When strict 'vars' is in scope, I<base> also lets you assign to @ISA
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178without having to declare @ISA with the 'vars' pragma first.
179
b8bc843f 180If any of the base classes are not loaded yet, I<base> silently
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181C<require>s them (but it won't call the C<import> method). Whether to
182C<require> a base class package is determined by the absence of a global
183$VERSION in the base package. If $VERSION is not detected even after
184loading it, I<base> will define $VERSION in the base package, setting it to
185the string C<-1, set by base.pm>.
b8bc843f 186
dc6d0c4f 187
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188=head1 HISTORY
189
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190This module was introduced with Perl 5.004_04.
191
fb73857a 192
dc6d0c4f 193=head1 CAVEATS
fb73857a 194
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195Due to the limitations of the pseudo-hash implementation, you must use
196base I<before> you declare any of your own fields.
17f410f9 197
fb73857a 198
dc6d0c4f 199=head1 SEE ALSO
fb73857a 200
dc6d0c4f 201L<fields>
fb73857a 202
dc6d0c4f 203=cut