# anything unless called on UNIVERSAL.
sub import {
return unless $_[0] eq __PACKAGE__;
+ require warnings;
+ warnings::warnif(
+ 'deprecated',
+ 'UNIVERSAL->import is deprecated and will be removed in a future perl',
+ );
goto &Exporter::import;
}
=item C<$obj>
-is a blessed reference or a string containing a package name
+is a blessed reference or a package name
=item C<CLASS>
=back
+=head1 WARNINGS
+
+B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
+C<isa> uses a very similar method and cache-ing strategy. This may cause
+strange effects if the Perl code dynamically changes @ISA in any package.
+
+You may add other methods to the UNIVERSAL class via Perl or XS code.
+You do not need to C<use UNIVERSAL> to make these methods
+available to your program (and you should not do so).
+
=head1 EXPORTS
None by default.
You may request the import of three functions (C<isa>, C<can>, and C<VERSION>),
-however it is usually harmful to do so. Please don't do this in new code.
+B<but this feature is deprecated and will be removed>. Please don't do this in
+new code.
For example, previous versions of this documentation suggested using C<isa> as
a function to determine the type of a reference: