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package base;
use strict 'vars';
use vars qw($VERSION);
$VERSION = '2.18';
$VERSION = eval $VERSION;
# 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( ($fglob && 'GLOB' eq ref($fglob) && *$fglob{HASH}) ? 1 : 0 );
}
sub has_attr {
my($proto) = shift;
my($class) = ref $proto || $proto;
return exists $Fattr->{$class};
}
sub get_attr {
$Fattr->{$_[0]} = [1] unless $Fattr->{$_[0]};
return $Fattr->{$_[0]};
}
if ($] < 5.009) {
*get_fields = sub {
# Shut up a possible typo warning.
() = \%{$_[0].'::FIELDS'};
my $f = \%{$_[0].'::FIELDS'};
# should be centralized in fields? perhaps
# fields::mk_FIELDS_be_OK. Peh. As long as %{ $package . '::FIELDS' }
# is used here anyway, it doesn't matter.
bless $f, 'pseudohash' if (ref($f) ne 'pseudohash');
return $f;
}
}
else {
*get_fields = sub {
# Shut up a possible typo warning.
() = \%{$_[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);
my @bases;
foreach my $base (@_) {
if ( $inheritor eq $base ) {
warn "Class '$inheritor' tried to inherit from itself\n";
}
next if grep $_->isa($base), ($inheritor, @bases);
# Following blocks help isolate $SIG{__DIE__} changes
{
my $sigdie;
{
local $SIG{__DIE__};
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;
local $" = " ";
Carp::croak(<<ERROR);
Base class package "$base" is empty.
(Perhaps you need to 'use' the module which defines that package first,
or make that module available in \@INC (\@INC contains: @INC).
ERROR
}
$sigdie = $SIG{__DIE__} || undef;
}
# Make sure a global $SIG{__DIE__} makes it out of the localization.
$SIG{__DIE__} = $sigdie if defined $sigdie;
}
push @bases, $base;
if ( has_fields($base) || has_attr($base) ) {
# No multiple fields inheritance *suck*
if ($fields_base) {
require Carp;
Carp::croak("Can't multiply inherit fields");
} else {
$fields_base = $base;
}
}
}
# Save this until the end so it's all or nothing if the above loop croaks.
push @{"$inheritor\::ISA"}, @bases;
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 <<"END";
$derived is inheriting from $base but already has its own fields!
This will cause problems. Be sure you use base BEFORE declaring fields.
END
}
# Iterate through the base's fields adding all the non-private
# ones to the derived class. Hang on to the original attribute
# (Public, Private, etc...) and add Inherited.
# This is all too complicated to do efficiently with add_fields().
while (my($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;
}
}
foreach my $idx (1..$#{$battr}) {
next if defined $dattr->[$idx];
$dattr->[$idx] = $battr->[$idx] & INHERITED;
}
}
1;
__END__
=head1 NAME
base - Establish an ISA relationship with base classes at compile time
=head1 SYNOPSIS
package Baz;
use base qw(Foo Bar);
=head1 DESCRIPTION
Unless you are using the C<fields> pragma, consider this module discouraged
in favor of the lighter-weight C<parent>.
Allows you to both load one or more modules, while setting up inheritance from
those modules at the same time. Roughly similar in effect to
package Baz;
BEGIN {
require Foo;
require Bar;
push @ISA, qw(Foo Bar);
}
When C<base> tries to C<require> a module, it will not die if it cannot find
the module's file, but will die on any other error. After all this, should
your base class be empty, containing no symbols, C<base> will die. This is
useful for inheriting from classes in the same file as yourself but where
the filename does not match the base module name, like so:
# in Bar.pm
package Foo;
sub exclaim { "I can have such a thing?!" }
package Bar;
use base "Foo";
There is no F<Foo.pm>, but because C<Foo> defines a symbol (the C<exclaim>
subroutine), C<base> will not die when the C<require> fails to load F<Foo.pm>.
C<base> will also initialize the fields if one of the base classes has it.
Multiple inheritance of fields is B<NOT> supported, if two or more base classes
each have inheritable fields the 'base' pragma will croak. See L<fields>
for a description of this feature.
The base class' C<import> method is B<not> called.
=head1 DIAGNOSTICS
=over 4
=item Base class package "%s" is empty.
base.pm was unable to require the base package, because it was not
found in your path.
=item Class 'Foo' tried to inherit from itself
Attempting to inherit from yourself generates a warning.
package Foo;
use base 'Foo';
=back
=head1 HISTORY
This module was introduced with Perl 5.004_04.
=head1 CAVEATS
Due to the limitations of the implementation, you must use
base I<before> you declare any of your own fields.
=head1 SEE ALSO
L<fields>
=cut
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