X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FUNIVERSAL.pm;h=92b4fcd352a812ab290ee32ed4009c79d31f33a6;hb=6ae21c79a25827be4ba4b5b312adea799e492b9a;hp=6d832c4bea283abd8212c2151971c95d1ce05289;hpb=a66bc3b0c7b47b1405c3f62393e8f35e9a4bbdb8;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/lib/UNIVERSAL.pm b/lib/UNIVERSAL.pm
index 6d832c4..92b4fcd 100644
--- a/lib/UNIVERSAL.pm
+++ b/lib/UNIVERSAL.pm
@@ -1,8 +1,16 @@
 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 can);
+*import = \&Exporter::import;
+@EXPORT_OK = qw(isa can VERSION);
 
 1;
 __END__
@@ -13,76 +21,98 @@ UNIVERSAL - base class for ALL classes (blessed references)
 
 =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>.
+   require UNIVERSAL ;
+   $yes = UNIVERSAL::isa $a, "ARRAY";
 
-C<VERSION> can be called as either a static or object method call.
+, 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".
 
-=back
+=item $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD )
 
-C<UNIVERSAL> also optionally exports the following subroutines
+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>.
 
-=over 4
+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.
 
-=item isa ( VAL, TYPE )
+C<can> can be called as a class (static) method, an object method, or a
+function.
 
-C<isa> returns I<true> if the first argument is a reference and either
-of the following statements is true.
+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.
 
-=over 8
-
-=item
+=item VERSION ( [ REQUIRE ] )
 
-C<VAL> 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<VAL> is a reference to a C<TYPE> of perl variable (er 'HASH')
 
 =back
 
-=item can ( VAL, METHOD )
+These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>.
+If you want simple local access to them you can do
 
-If C<VAL> is a blessed reference 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.
+  *isa = \&UNIVERSAL::isa;
 
-=back
+to import isa into your package.
 
 =cut