| 1 | package base; |
| 2 | |
| 3 | use strict 'vars'; |
| 4 | use vars qw($VERSION); |
| 5 | $VERSION = '2.07'; |
| 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}; |
| 21 | return( ($fglob && *$fglob{HASH}) ? 1 : 0 ); |
| 22 | } |
| 23 | |
| 24 | sub has_version { |
| 25 | my($base) = shift; |
| 26 | my $vglob = ${$base.'::'}{VERSION}; |
| 27 | return( ($vglob && *$vglob{SCALAR}) ? 1 : 0 ); |
| 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 | |
| 41 | if ($] < 5.009) { |
| 42 | *get_fields = sub { |
| 43 | # Shut up a possible typo warning. |
| 44 | () = \%{$_[0].'::FIELDS'}; |
| 45 | my $f = \%{$_[0].'::FIELDS'}; |
| 46 | |
| 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 | } |
| 61 | } |
| 62 | |
| 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 (@_) { |
| 74 | next if $inheritor->isa($base); |
| 75 | |
| 76 | if (has_version($base)) { |
| 77 | ${$base.'::VERSION'} = '-1, set by base.pm' |
| 78 | unless defined ${$base.'::VERSION'}; |
| 79 | } |
| 80 | else { |
| 81 | local $SIG{__DIE__}; |
| 82 | eval "require $base"; |
| 83 | # Only ignore "Can't locate" errors from our eval require. |
| 84 | # Other fatal errors (syntax etc) must be reported. |
| 85 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
| 86 | unless (%{"$base\::"}) { |
| 87 | require Carp; |
| 88 | Carp::croak(<<ERROR); |
| 89 | Base class package "$base" is empty. |
| 90 | (Perhaps you need to 'use' the module which defines that package first.) |
| 91 | ERROR |
| 92 | |
| 93 | } |
| 94 | ${$base.'::VERSION'} = "-1, set by base.pm" |
| 95 | unless defined ${$base.'::VERSION'}; |
| 96 | } |
| 97 | push @{"$inheritor\::ISA"}, $base; |
| 98 | |
| 99 | if ( has_fields($base) || has_attr($base) ) { |
| 100 | # No multiple fields inheritance *suck* |
| 101 | if ($fields_base) { |
| 102 | require Carp; |
| 103 | Carp::croak("Can't multiply inherit %FIELDS"); |
| 104 | } else { |
| 105 | $fields_base = $base; |
| 106 | } |
| 107 | } |
| 108 | } |
| 109 | |
| 110 | if( defined $fields_base ) { |
| 111 | inherit_fields($inheritor, $fields_base); |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | |
| 116 | sub inherit_fields { |
| 117 | my($derived, $base) = @_; |
| 118 | |
| 119 | return SUCCESS unless $base; |
| 120 | |
| 121 | my $battr = get_attr($base); |
| 122 | my $dattr = get_attr($derived); |
| 123 | my $dfields = get_fields($derived); |
| 124 | my $bfields = get_fields($base); |
| 125 | |
| 126 | $dattr->[0] = @$battr; |
| 127 | |
| 128 | if( keys %$dfields ) { |
| 129 | warn "$derived is inheriting from $base but already has its own ". |
| 130 | "fields!\n". |
| 131 | "This will cause problems.\n". |
| 132 | "Be sure you use base BEFORE declaring fields\n"; |
| 133 | } |
| 134 | |
| 135 | # Iterate through the base's fields adding all the non-private |
| 136 | # ones to the derived class. Hang on to the original attribute |
| 137 | # (Public, Private, etc...) and add Inherited. |
| 138 | # This is all too complicated to do efficiently with add_fields(). |
| 139 | while (my($k,$v) = each %$bfields) { |
| 140 | my $fno; |
| 141 | if ($fno = $dfields->{$k} and $fno != $v) { |
| 142 | require Carp; |
| 143 | Carp::croak ("Inherited %FIELDS can't override existing %FIELDS"); |
| 144 | } |
| 145 | |
| 146 | if( $battr->[$v] & PRIVATE ) { |
| 147 | $dattr->[$v] = PRIVATE | INHERITED; |
| 148 | } |
| 149 | else { |
| 150 | $dattr->[$v] = INHERITED | $battr->[$v]; |
| 151 | $dfields->{$k} = $v; |
| 152 | } |
| 153 | } |
| 154 | |
| 155 | foreach my $idx (1..$#{$battr}) { |
| 156 | next if defined $dattr->[$idx]; |
| 157 | $dattr->[$idx] = $battr->[$idx] & INHERITED; |
| 158 | } |
| 159 | } |
| 160 | |
| 161 | |
| 162 | 1; |
| 163 | |
| 164 | __END__ |
| 165 | |
| 166 | =head1 NAME |
| 167 | |
| 168 | base - Establish IS-A relationship with base classes at compile time |
| 169 | |
| 170 | =head1 SYNOPSIS |
| 171 | |
| 172 | package Baz; |
| 173 | use base qw(Foo Bar); |
| 174 | |
| 175 | =head1 DESCRIPTION |
| 176 | |
| 177 | Allows you to both load one or more modules, while setting up inheritance from |
| 178 | those modules at the same time. Roughly similar in effect to |
| 179 | |
| 180 | package Baz; |
| 181 | BEGIN { |
| 182 | require Foo; |
| 183 | require Bar; |
| 184 | push @ISA, qw(Foo Bar); |
| 185 | } |
| 186 | |
| 187 | If any of the listed modules are not loaded yet, I<base> silently attempts to |
| 188 | C<require> them (and silently continues if the C<require> failed). Whether to |
| 189 | C<require> a base class module is determined by the absence of a global variable |
| 190 | $VERSION in the base package. If $VERSION is not detected even after loading |
| 191 | it, <base> will define $VERSION in the base package, setting it to the string |
| 192 | C<-1, set by base.pm>. |
| 193 | |
| 194 | Will also initialize the fields if one of the base classes has it. |
| 195 | Multiple inheritance of fields is B<NOT> supported, if two or more |
| 196 | base classes each have inheritable fields the 'base' pragma will |
| 197 | croak. See L<fields>, L<public> and L<protected> for a description of |
| 198 | this feature. |
| 199 | |
| 200 | =head1 DIAGNOSTICS |
| 201 | |
| 202 | =over 4 |
| 203 | |
| 204 | =item Base class package "%s" is empty. |
| 205 | |
| 206 | base.pm was unable to require the base package, because it was not |
| 207 | found in your path. |
| 208 | |
| 209 | =back |
| 210 | |
| 211 | =head1 HISTORY |
| 212 | |
| 213 | This module was introduced with Perl 5.004_04. |
| 214 | |
| 215 | |
| 216 | =head1 CAVEATS |
| 217 | |
| 218 | Due to the limitations of the implementation, you must use |
| 219 | base I<before> you declare any of your own fields. |
| 220 | |
| 221 | |
| 222 | =head1 SEE ALSO |
| 223 | |
| 224 | L<fields> |
| 225 | |
| 226 | =cut |