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=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);
    }
Will also initialize the %FIELDS hash if one of the base classes has
it.  Multiple inheritance of %FIELDS is not supported.  The 'base'
pragma will croak if multiple base classes has a %FIELDS hash.  See
L<fields> for a description of this feature.
When strict 'vars' is in scope I<base> also let you assign to @ISA
without having to declare @ISA with the 'vars' pragma first.
This module was introduced with Perl 5.004_04.
=head1 SEE ALSO
L<fields>
=cut
package base;
sub import {
    my $class = shift;
    my $fields_base;
    foreach my $base (@_) {
        unless (defined %{"$base\::"}) {
            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 (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.)");
            }
        }
        # A simple test like (defined %{"$base\::FIELDS"}) will
        # sometimes produce typo warnings because it would create
        # the hash if it was not present before.
        my $fglob;
        if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) {
            if ($fields_base) {
                require Carp;
                Carp::croak("Can't multiply inherit %FIELDS");
            } else {
                $fields_base = $base;
            }
        }
    }
    my $pkg = caller(0);
    push @{"$pkg\::ISA"}, @_;
    if ($fields_base) {
        require fields;
        fields::inherit($pkg, $fields_base);
    }
}
1;