| 1 | package base; |
| 2 | |
| 3 | use strict 'vars'; |
| 4 | use vars qw($VERSION); |
| 5 | $VERSION = '2.14'; |
| 6 | $VERSION = eval $VERSION; |
| 7 | |
| 8 | # constant.pm is slow |
| 9 | sub SUCCESS () { 1 } |
| 10 | |
| 11 | sub PUBLIC () { 2**0 } |
| 12 | sub PRIVATE () { 2**1 } |
| 13 | sub INHERITED () { 2**2 } |
| 14 | sub PROTECTED () { 2**3 } |
| 15 | |
| 16 | |
| 17 | my $Fattr = \%fields::attr; |
| 18 | |
| 19 | sub has_fields { |
| 20 | my($base) = shift; |
| 21 | my $fglob = ${"$base\::"}{FIELDS}; |
| 22 | return( ($fglob && 'GLOB' eq ref($fglob) && *$fglob{HASH}) ? 1 : 0 ); |
| 23 | } |
| 24 | |
| 25 | sub has_version { |
| 26 | my($base) = shift; |
| 27 | my $vglob = ${$base.'::'}{VERSION}; |
| 28 | return( ($vglob && *$vglob{SCALAR}) ? 1 : 0 ); |
| 29 | } |
| 30 | |
| 31 | sub has_attr { |
| 32 | my($proto) = shift; |
| 33 | my($class) = ref $proto || $proto; |
| 34 | return exists $Fattr->{$class}; |
| 35 | } |
| 36 | |
| 37 | sub get_attr { |
| 38 | $Fattr->{$_[0]} = [1] unless $Fattr->{$_[0]}; |
| 39 | return $Fattr->{$_[0]}; |
| 40 | } |
| 41 | |
| 42 | if ($] < 5.009) { |
| 43 | *get_fields = sub { |
| 44 | # Shut up a possible typo warning. |
| 45 | () = \%{$_[0].'::FIELDS'}; |
| 46 | my $f = \%{$_[0].'::FIELDS'}; |
| 47 | |
| 48 | # should be centralized in fields? perhaps |
| 49 | # fields::mk_FIELDS_be_OK. Peh. As long as %{ $package . '::FIELDS' } |
| 50 | # is used here anyway, it doesn't matter. |
| 51 | bless $f, 'pseudohash' if (ref($f) ne 'pseudohash'); |
| 52 | |
| 53 | return $f; |
| 54 | } |
| 55 | } |
| 56 | else { |
| 57 | *get_fields = sub { |
| 58 | # Shut up a possible typo warning. |
| 59 | () = \%{$_[0].'::FIELDS'}; |
| 60 | return \%{$_[0].'::FIELDS'}; |
| 61 | } |
| 62 | } |
| 63 | |
| 64 | sub import { |
| 65 | my $class = shift; |
| 66 | |
| 67 | return SUCCESS unless @_; |
| 68 | |
| 69 | # List of base classes from which we will inherit %FIELDS. |
| 70 | my $fields_base; |
| 71 | |
| 72 | my $inheritor = caller(0); |
| 73 | my @isa_classes; |
| 74 | |
| 75 | my @bases; |
| 76 | foreach my $base (@_) { |
| 77 | if ( $inheritor eq $base ) { |
| 78 | warn "Class '$inheritor' tried to inherit from itself\n"; |
| 79 | } |
| 80 | |
| 81 | next if grep $_->isa($base), ($inheritor, @bases); |
| 82 | |
| 83 | if (has_version($base)) { |
| 84 | ${$base.'::VERSION'} = '-1, set by base.pm' |
| 85 | unless defined ${$base.'::VERSION'}; |
| 86 | } |
| 87 | else { |
| 88 | my $sigdie; |
| 89 | { |
| 90 | local $SIG{__DIE__}; |
| 91 | eval "require $base"; |
| 92 | # Only ignore "Can't locate" errors from our eval require. |
| 93 | # Other fatal errors (syntax etc) must be reported. |
| 94 | die if $@ && $@ !~ /^Can't locate .*? at \(eval /; |
| 95 | unless (%{"$base\::"}) { |
| 96 | require Carp; |
| 97 | local $" = " "; |
| 98 | Carp::croak(<<ERROR); |
| 99 | Base class package "$base" is empty. |
| 100 | (Perhaps you need to 'use' the module which defines that package first, |
| 101 | or make that module available in \@INC (\@INC contains: @INC). |
| 102 | ERROR |
| 103 | } |
| 104 | $sigdie = $SIG{__DIE__} || undef; |
| 105 | } |
| 106 | # Make sure a global $SIG{__DIE__} makes it out of the localization. |
| 107 | $SIG{__DIE__} = $sigdie if defined $sigdie; |
| 108 | ${$base.'::VERSION'} = "-1, set by base.pm" |
| 109 | unless defined ${$base.'::VERSION'}; |
| 110 | } |
| 111 | push @bases, $base; |
| 112 | |
| 113 | if ( has_fields($base) || has_attr($base) ) { |
| 114 | # No multiple fields inheritance *suck* |
| 115 | if ($fields_base) { |
| 116 | require Carp; |
| 117 | Carp::croak("Can't multiply inherit fields"); |
| 118 | } else { |
| 119 | $fields_base = $base; |
| 120 | } |
| 121 | } |
| 122 | } |
| 123 | # Save this until the end so it's all or nothing if the above loop croaks. |
| 124 | push @{"$inheritor\::ISA"}, @isa_classes; |
| 125 | |
| 126 | push @{"$inheritor\::ISA"}, @bases; |
| 127 | |
| 128 | if( defined $fields_base ) { |
| 129 | inherit_fields($inheritor, $fields_base); |
| 130 | } |
| 131 | } |
| 132 | |
| 133 | |
| 134 | sub inherit_fields { |
| 135 | my($derived, $base) = @_; |
| 136 | |
| 137 | return SUCCESS unless $base; |
| 138 | |
| 139 | my $battr = get_attr($base); |
| 140 | my $dattr = get_attr($derived); |
| 141 | my $dfields = get_fields($derived); |
| 142 | my $bfields = get_fields($base); |
| 143 | |
| 144 | $dattr->[0] = @$battr; |
| 145 | |
| 146 | if( keys %$dfields ) { |
| 147 | warn <<"END"; |
| 148 | $derived is inheriting from $base but already has its own fields! |
| 149 | This will cause problems. Be sure you use base BEFORE declaring fields. |
| 150 | END |
| 151 | |
| 152 | } |
| 153 | |
| 154 | # Iterate through the base's fields adding all the non-private |
| 155 | # ones to the derived class. Hang on to the original attribute |
| 156 | # (Public, Private, etc...) and add Inherited. |
| 157 | # This is all too complicated to do efficiently with add_fields(). |
| 158 | while (my($k,$v) = each %$bfields) { |
| 159 | my $fno; |
| 160 | if ($fno = $dfields->{$k} and $fno != $v) { |
| 161 | require Carp; |
| 162 | Carp::croak ("Inherited fields can't override existing fields"); |
| 163 | } |
| 164 | |
| 165 | if( $battr->[$v] & PRIVATE ) { |
| 166 | $dattr->[$v] = PRIVATE | INHERITED; |
| 167 | } |
| 168 | else { |
| 169 | $dattr->[$v] = INHERITED | $battr->[$v]; |
| 170 | $dfields->{$k} = $v; |
| 171 | } |
| 172 | } |
| 173 | |
| 174 | foreach my $idx (1..$#{$battr}) { |
| 175 | next if defined $dattr->[$idx]; |
| 176 | $dattr->[$idx] = $battr->[$idx] & INHERITED; |
| 177 | } |
| 178 | } |
| 179 | |
| 180 | |
| 181 | 1; |
| 182 | |
| 183 | __END__ |
| 184 | |
| 185 | =head1 NAME |
| 186 | |
| 187 | base - Establish an ISA relationship with base classes at compile time |
| 188 | |
| 189 | =head1 SYNOPSIS |
| 190 | |
| 191 | package Baz; |
| 192 | use base qw(Foo Bar); |
| 193 | |
| 194 | =head1 DESCRIPTION |
| 195 | |
| 196 | Unless you are using the C<fields> pragma, consider this module discouraged |
| 197 | in favor of the lighter-weight C<parent>. |
| 198 | |
| 199 | Allows you to both load one or more modules, while setting up inheritance from |
| 200 | those modules at the same time. Roughly similar in effect to |
| 201 | |
| 202 | package Baz; |
| 203 | BEGIN { |
| 204 | require Foo; |
| 205 | require Bar; |
| 206 | push @ISA, qw(Foo Bar); |
| 207 | } |
| 208 | |
| 209 | C<base> employs some heuristics to determine if a module has already been |
| 210 | loaded, if it has it doesn't try again. If C<base> tries to C<require> the |
| 211 | module it will not die if it cannot find the module's file, but will die on any |
| 212 | other error. After all this, should your base class be empty, containing no |
| 213 | symbols, it will die. This is useful for inheriting from classes in the same |
| 214 | file as yourself, like so: |
| 215 | |
| 216 | package Foo; |
| 217 | sub exclaim { "I can have such a thing?!" } |
| 218 | |
| 219 | package Bar; |
| 220 | use base "Foo"; |
| 221 | |
| 222 | If $VERSION is not detected even after loading it, <base> will define $VERSION |
| 223 | in the base package, setting it to the string C<-1, set by base.pm>. |
| 224 | |
| 225 | C<base> will also initialize the fields if one of the base classes has it. |
| 226 | Multiple inheritance of fields is B<NOT> supported, if two or more base classes |
| 227 | each have inheritable fields the 'base' pragma will croak. See L<fields>, |
| 228 | L<public> and L<protected> for a description of this feature. |
| 229 | |
| 230 | The base class' C<import> method is B<not> called. |
| 231 | |
| 232 | |
| 233 | =head1 DIAGNOSTICS |
| 234 | |
| 235 | =over 4 |
| 236 | |
| 237 | =item Base class package "%s" is empty. |
| 238 | |
| 239 | base.pm was unable to require the base package, because it was not |
| 240 | found in your path. |
| 241 | |
| 242 | =item Class 'Foo' tried to inherit from itself |
| 243 | |
| 244 | Attempting to inherit from yourself generates a warning. |
| 245 | |
| 246 | use Foo; |
| 247 | use base 'Foo'; |
| 248 | |
| 249 | =back |
| 250 | |
| 251 | =head1 HISTORY |
| 252 | |
| 253 | This module was introduced with Perl 5.004_04. |
| 254 | |
| 255 | =head1 CAVEATS |
| 256 | |
| 257 | Due to the limitations of the implementation, you must use |
| 258 | base I<before> you declare any of your own fields. |
| 259 | |
| 260 | |
| 261 | =head1 SEE ALSO |
| 262 | |
| 263 | L<fields> |
| 264 | |
| 265 | =cut |