source: trunk/essentials/dev-lang/perl/lib/UNIVERSAL.pm@ 3951

package UNIVERSAL;

our $VERSION = '1.01';

# UNIVERSAL should not contain any extra subs/methods beyond those
# that it exists to define. The use of Exporter below is a historical
# accident that can't be fixed without breaking code.  Note that we
# *don't* set @ISA here, don't want all classes/objects inheriting from
# Exporter.  It's bad enough that all classes have a import() method
# whenever UNIVERSAL.pm is loaded.
require Exporter;
*import = \&Exporter::import;
@EXPORT_OK = qw(isa can VERSION);

1;
__END__

=head1 NAME

UNIVERSAL - base class for ALL classes (blessed references)

=head1 SYNOPSIS

    $is_io = $fd->isa("IO::Handle");
    $is_io = Class->isa("IO::Handle");

    $sub = $obj->can("print");
    $sub = Class->can("print");

    use UNIVERSAL qw( isa can VERSION );
    $yes = isa $ref, "HASH" ;
    $sub = can $ref, "fandango" ;
    $ver = VERSION $obj ;

=head1 DESCRIPTION

C<UNIVERSAL> is the base class which all bless references will inherit from,
see L<perlobj>.

C<UNIVERSAL> provides the following methods and functions:

=over 4

=item C<< $obj->isa( TYPE ) >>

=item C<< CLASS->isa( TYPE ) >> 

=item C<isa( VAL, TYPE )>

Where

=over 4

=item C<TYPE>

is a package name

=item C<$obj>

is a blessed reference or a string containing a package name

=item C<CLASS>

is a package name

=item C<VAL>

is any of the above or an unblessed reference

=back

When used as an instance or class method (C<< $obj->isa( TYPE ) >>),
C<isa> returns I<true> if $obj is blessed into package C<TYPE> or
inherits from package C<TYPE>.

When used as a class method (C<< CLASS->isa( TYPE ) >>: sometimes
referred to as a static method), C<isa> returns I<true> if C<CLASS>
inherits from (or is itself) the name of the package C<TYPE> or
inherits from package C<TYPE>.

When used as a function, like

   use UNIVERSAL qw( isa ) ;
   $yes = isa $h, "HASH";