+package base;
+
+use strict 'vars';
+use vars qw($VERSION);
+$VERSION = '2.03';
+
+# constant.pm is slow
+sub SUCCESS () { 1 }
+
+sub PUBLIC () { 2**0 }
+sub PRIVATE () { 2**1 }
+sub INHERITED () { 2**2 }
+sub PROTECTED () { 2**3 }
+
+
+my $Fattr = \%fields::attr;
+
+sub has_fields {
+ my($base) = shift;
+ my $fglob = ${"$base\::"}{FIELDS};
+ return( ($fglob && *$fglob{HASH}) ? 1 : 0 );
+}
+
+sub has_version {
+ my($base) = shift;
+ my $vglob = ${$base.'::'}{VERSION};
+ return( ($vglob && *$vglob{SCALAR}) ? 1 : 0 );
+}
+
+sub has_attr {
+ my($proto) = shift;
+ my($class) = ref $proto || $proto;
+ return exists $Fattr->{$class};
+}
+
+sub get_attr {
+ $Fattr->{$_[0]} = [1] unless $Fattr->{$_[0]};
+ return $Fattr->{$_[0]};
+}
+
+sub get_fields {
+ # Shut up a possible typo warning.
+ () = \%{$_[0].'::FIELDS'};
+
+ return \%{$_[0].'::FIELDS'};
+}
+
+sub import {
+ my $class = shift;
+
+ return SUCCESS unless @_;
+
+ # List of base classes from which we will inherit %FIELDS.
+ my $fields_base;
+
+ my $inheritor = caller(0);
+
+ foreach my $base (@_) {
+ next if $inheritor->isa($base);
+
+ if (has_version($base)) {
+ ${$base.'::VERSION'} = '-1, set by base.pm'
+ unless defined ${$base.'::VERSION'};
+ }
+ else {
+ local $SIG{__DIE__} = 'IGNORE';
+ eval "require $base";
+ # Only ignore "Can't locate" errors from our eval require.
+ # Other fatal errors (syntax etc) must be reported.
+ die if $@ && $@ !~ /^Can't locate .*? at \(eval /;
+ unless (%{"$base\::"}) {
+ require Carp;
+ Carp::croak(<<ERROR);
+Base class package "$base" is empty.
+ (Perhaps you need to 'use' the module which defines that package first.)
+ERROR
+
+ }
+ ${$base.'::VERSION'} = "-1, set by base.pm"
+ unless defined ${$base.'::VERSION'};
+ }
+ push @{"$inheritor\::ISA"}, $base;
+
+ if ( has_fields($base) || has_attr($base) ) {
+ # No multiple fields inheritence *suck*
+ if ($fields_base) {
+ require Carp;
+ Carp::croak("Can't multiply inherit %FIELDS");
+ } else {
+ $fields_base = $base;
+ }
+ }
+ }
+
+ if( defined $fields_base ) {
+ inherit_fields($inheritor, $fields_base);
+ }
+}
+
+
+sub inherit_fields {
+ my($derived, $base) = @_;
+
+ return SUCCESS unless $base;
+
+ my $battr = get_attr($base);
+ my $dattr = get_attr($derived);
+ my $dfields = get_fields($derived);
+ my $bfields = get_fields($base);
+
+ $dattr->[0] = @$battr;
+
+ if( keys %$dfields ) {
+ warn "$derived is inheriting from $base but already has its own ".
+ "fields!\n".
+ "This will cause problems with pseudo-hashes.\n".
+ "Be sure you use base BEFORE declaring fields\n";
+ }
+
+ # Iterate through the base's fields adding all the non-private
+ # ones to the derived class. Hang on to the original attribute
+ # (Public, Private, etc...) and add Inherited.
+ # This is all too complicated to do efficiently with add_fields().
+ while (my($k,$v) = each %$bfields) {
+ my $fno;
+ if ($fno = $dfields->{$k} and $fno != $v) {
+ require Carp;
+ Carp::croak ("Inherited %FIELDS can't override existing %FIELDS");
+ }
+
+ if( $battr->[$v] & PRIVATE ) {
+ $dattr->[$v] = PRIVATE | INHERITED;
+ }
+ else {
+ $dattr->[$v] = INHERITED | $battr->[$v];
+ $dfields->{$k} = $v;
+ }
+ }
+
+ unless( keys %$bfields ) {
+ foreach my $idx (1..$#{$battr}) {
+ $dattr->[$idx] = $battr->[$idx] & INHERITED;
+ }
+ }
+}
+
+
+1;
+
+__END__
+
=head1 NAME
base - Establish IS-A relationship with base class at compile time
=head1 SYNOPSIS
package Baz;
-
use base qw(Foo Bar);
=head1 DESCRIPTION
Roughly similar in effect to
BEGIN {
- require Foo;
- require Bar;
- push @ISA, qw(Foo Bar);
+ require Foo;
+ require Bar;
+ push @ISA, qw(Foo Bar);
}
+Will also initialize the fields if one of the base classes has it.
+Multiple Inheritence of fields is B<NOT> supported, if two or more
+base classes each have inheritable fields the 'base' pragma will
+croak. See L<fields>, L<public> and L<protected> for a description of
+this feature.
+
+When strict 'vars' is in scope, I<base> also lets you assign to @ISA
+without having to declare @ISA with the 'vars' pragma first.
+
+If any of the base classes are not loaded yet, I<base> silently
+C<require>s them (but it won't call the C<import> method). Whether to
+C<require> a base class package is determined by the absence of a global
+$VERSION in the base package. If $VERSION is not detected even after
+loading it, I<base> will define $VERSION in the base package, setting it to
+the string C<-1, set by base.pm>.
+
+
+=head1 HISTORY
+
This module was introduced with Perl 5.004_04.
-=head1 BUGS
-Needs proper documentation!
+=head1 CAVEATS
-=cut
+Due to the limitations of the pseudo-hash implementation, you must use
+base I<before> you declare any of your own fields.
-package base;
-sub import {
- my $class = shift;
+=head1 SEE ALSO
- foreach my $base (@_) {
- unless (defined %{"$base\::"}) {
- eval "require $base";
- unless (defined %{"$base\::"}) {
- require Carp;
- Carp::croak("Base class package \"$base\" is empty.\n",
- "\t(Perhaps you need to 'use' the module ",
- "which defines that package first.)");
- }
- }
- }
-
- push @{caller(0) . '::ISA'}, @_;
-}
+L<fields>
-1;
+=cut
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