Here's a variant of the previous patch with feedback incorporated. The only change is to the perlfunc patch, to make the possibilities and strengths and weaknesses of each approach more explicit.
-- c
--- pod/perlfunc.pod~ 2005-06-15 11:43:41.000000000 -0700 +++ pod/perlfunc.pod 2005-06-15 11:46:27.000000000 -0700 @@ -1158,9 +1158,11 @@ is sometimes preferable to matching particular string values of $@ using regular expressions. Here's an example: + use Scalar::Util 'blessed'; + eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) }; if ($@) { - if (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) { + if (blessed($@) && [EMAIL PROTECTED]>isa("Some::Module::Exception")) { # handle Some::Module::Exception } else { @@ -4195,9 +4197,6 @@ unless (ref($r)) { print "r is not a reference at all.\n"; } - if (UNIVERSAL::isa($r, "HASH")) { # for subclassing - print "r is a reference to something that isa hash.\n"; - } See also L<perlref>. --- pod/perlobj.pod~ 2005-06-15 11:47:01.000000000 -0700 +++ pod/perlobj.pod 2005-06-15 11:50:34.000000000 -0700 @@ -373,18 +373,19 @@ C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS> -You can also call C<UNIVERSAL::isa> as a subroutine with two arguments. -The first does not need to be an object or even a reference. This -allows you to check what a reference points to, or whether -something is a reference of a given type. Example +You can also call C<UNIVERSAL::isa> as a subroutine with two arguments. Of +course, this will do the wrong thing if someone has overridden C<isa> in a +class, so don't do it. - if(UNIVERSAL::isa($ref, 'ARRAY')) { - #... - } +If you need to determine whether you've received a valid invocant, use the +C<blessed> function from L<Scalar::Util>: -To determine if a reference is a blessed object, you can write + if (blessed($ref) && $ref->isa( 'Some::Class')) { + # ... + } - print "It's an object\n" if UNIVERSAL::isa($val, 'UNIVERSAL'); +C<blessed> returns the name of the package the argument has been +blessed into, or C<undef>. =item can(METHOD) @@ -392,21 +393,9 @@ if it does then a reference to the sub is returned, if it does not then I<undef> is returned. -C<UNIVERSAL::can> can also be called as a subroutine with two arguments. -It'll always return I<undef> if its first argument isn't an object or a -class name. So here's another way to check if a reference is a -blessed object - - print "It's still an object\n" if UNIVERSAL::can($val, 'can'); - -You can also use the C<blessed> function of Scalar::Util: - - use Scalar::Util 'blessed'; - - my $blessing = blessed $suspected_object; - -C<blessed> returns the name of the package the argument has been -blessed into, or C<undef>. +C<UNIVERSAL::can> can also be called as a subroutine with two arguments. It'll +always return I<undef> if its first argument isn't an object or a class name. +The same caveats for calling C<UNIVERSAL::isa> directly apply here, too. =item VERSION( [NEED] ) --- pod/perltooc.pod~ 2005-06-15 11:51:14.000000000 -0700 +++ pod/perltooc.pod 2005-06-15 11:52:08.000000000 -0700 @@ -1089,7 +1089,10 @@ if (my $coderef = $self->can($parent . "::CData1")) { $self->$coderef($newvalue); } - } + } + +If you override C<UNIVERSAL::can> in your own classes, be sure to return the +reference appropriately. =head2 Locking the Door and Throwing Away the Key