package UNIVERSAL;
+our $VERSION = '1.00';
+
+# 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;
-@ISA = qw(Exporter);
-@EXPORT_OK = qw(isa);
+*import = \&Exporter::import;
+@EXPORT_OK = qw(isa can VERSION);
1;
__END__
=head1 SYNOPSIS
- use UNIVERSAL qw(isa);
+ $is_io = $fd->isa("IO::Handle");
+ $is_io = Class->isa("IO::Handle");
- $yes = isa($ref, "HASH");
- $io = $fd->isa("IO::Handle");
- $sub = $obj->can('print');
+ $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>
+see L<perlobj>.
-C<UNIVERSAL> provides the following methods
+C<UNIVERSAL> provides the following methods and functions:
=over 4
-=item isa ( TYPE )
+=item $obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, TYPE )
-C<isa> returns I<true> if C<REF> is blessed into package C<TYPE>
-or inherits from package C<TYPE>.
+ C<TYPE> is a package name
+ $obj is a blessed reference or a string containing a package name
+ C<CLASS> is a package name
+ C<VAL> is any of the above or an unblessed reference
-C<isa> can be called as either a static or object method call.
+When used as an instance or class method (C<$obj->isa( TYPE )>), C<isa>
+returns I<true> if $obj is blessed into package C<TYPE> or inherits from
+package C<TYPE>.
-=item can ( METHOD )
+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>.
-C<can> checks if the object has a method called C<METHOD>. If it does
-then a reference to the sub is returned. If it does not then I<undef>
-is returned.
+When used as a function, like
-C<can> can be called as either a static or object method call.
+ use UNIVERSAL qw( isa ) ;
+ $yes = isa $h, "HASH";
+ $yes = isa "Foo", "Bar";
-=item VERSION ( [ REQUIRE ] )
+or
-C<VERSION> will return the value of the variable C<$VERSION> in the
-package the object is blessed into. If C<REQUIRE> is given then
-it will do a comparison and die if the package version is not
-greater than or equal to C<REQUIRE>.
-
-C<VERSION> can be called as either a static or object method call.
+ require UNIVERSAL ;
+ $yes = UNIVERSAL::isa $a, "ARRAY";
-=back
+, C<isa> returns I<true> in the same cases as above and also if C<VAL> is an
+unblessed reference to a perl variable of type C<TYPE>, such as "HASH",
+"ARRAY", or "Regexp".
-C<UNIVERSAL> also optionally exports the following subroutines
+=item $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD )
-=over 4
+C<can> checks if the object or class has a method called C<METHOD>. If it does
+then a reference to the sub is returned. If it does not then I<undef> is
+returned. This includes methods inherited or imported by C<$obj>, C<CLASS>, or
+C<VAL>.
-=item isa ( REF, TYPE )
+C<can> cannot know whether an object will be able to provide a method
+through AUTOLOAD, so a return value of I<undef> does not necessarily mean
+the object will not be able to handle the method call. To get around
+this some module authors use a forward declaration (see L<perlsub>)
+for methods they will handle via AUTOLOAD. For such 'dummy' subs, C<can>
+will still return a code reference, which, when called, will fall through
+to the AUTOLOAD. If no suitable AUTOLOAD is provided, calling the coderef
+will cause an error.
-C<isa> returns I<true> if the first argument is a reference and either
-of the following statements is true.
+C<can> can be called as a class (static) method, an object method, or a
+function.
-=over 8
+When used as a function, if C<VAL> is a blessed reference or package name which
+has a method called C<METHOD>, C<can> returns a reference to the subroutine.
+If C<VAL> is not a blessed reference, or if it does not have a method
+C<METHOD>, I<undef> is returned.
-=item
+=item VERSION ( [ REQUIRE ] )
-C<REF> is a blessed reference and is blessed into package C<TYPE>
-or inherits from package C<TYPE>
+C<VERSION> will return the value of the variable C<$VERSION> in the
+package the object is blessed into. If C<REQUIRE> is given then
+it will do a comparison and die if the package version is not
+greater than or equal to C<REQUIRE>.
-=item
+C<VERSION> can be called as either a class (static) method, an object method or
+or a function.
-C<REF> is a reference to a C<TYPE> of perl variable (er 'HASH')
=back
-=back
+These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>.
+If you want simple local access to them you can do
+
+ *isa = \&UNIVERSAL::isa;
+
+to import isa into your package.
=cut
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