universal::isa(3pm) [debian man page]

UNIVERSAL::isa(3pm)					User Contributed Perl Documentation				       UNIVERSAL::isa(3pm)

NAME

       UNIVERSAL::isa - recover from people calling UNIVERSAL::isa as a function

SYNOPSIS

	   # from the shell
	   echo 'export PERL5OPT=-MUNIVERSAL::isa' >> /etc/profile

	   # within your program
	   use UNIVERSAL::isa;

	   # enable warnings for all dodgy uses of UNIVERSAL::isa
	   use UNIVERSAL::isa 'verbose';

DESCRIPTION

       Whenever you use "isa" in UNIVERSAL as a function, a kitten using Test::MockObject dies. Normally, the kittens would be helpless, but if
       they use UNIVERSAL::isa (the module whose docs you are reading), the kittens can live long and prosper.

       This module replaces "UNIVERSAL::isa" with a version that makes sure that, when called as a function on objects which override "isa", "isa"
       will call the appropriate method on those objects

       In all other cases, the real "UNIVERSAL::isa" gets called directly.

       NOTE: You should use this module only for debugging purposes. It does not belong as a dependency in running code.

WARNINGS

       If the lexical warnings pragma is available, this module will emit a warning for each naughty invocation of "UNIVERSAL::isa". Silence these
       warnings by saying:

	   no warnings 'UNIVERSAL::isa';

       in the lexical scope of the naughty code.

       After version 1.00, warnings only appear when naughty code calls UNIVERSAL::isa() as a function on an invocant for which there is an
       overridden isa().  These are really truly active bugs, and you should fix them rather than relying on this module to find them.

       To get warnings for all potentially dangerous uses of UNIVERSAL::isa() as a function, not a method (that is, for all uses of the method as
       a function, which are latent bugs, if not bugs that will break your code as it exists now), pass the "verbose" flag when using the module.
       This can generate many extra warnings, but they're more specific as to the actual wrong practice and they usually suggest proper fixes.

SEE ALSO

       Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalIsa

       UNIVERSAL::can for another discussion of the problem at hand.

       Test::MockObject for one example of a module that really needs to override "isa()".

       Any decent explanation of OO to understand why calling methods as functions is a staggeringly bad idea.

AUTHORS

       Audrey Tang <cpan@audreyt.org>

       chromatic <chromatic@wgz.org>

       Yuval Kogman <nothingmuch@woobling.org>

COPYRIGHT &; LICENSE
       Copyright (c) 2005 - 2011, chromatic. This module is made available under the same terms as Perl 5.12.

perl v5.14.2							    2012-04-18						       UNIVERSAL::isa(3pm)

UNIVERSAL(3pm)						 Perl Programmers Reference Guide					    UNIVERSAL(3pm)

NAME

       UNIVERSAL - base class for ALL classes (blessed references)

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 ;

DESCRIPTION

       "UNIVERSAL" is the base class which all bless references will inherit from, see perlobj.

       "UNIVERSAL" provides the following methods and functions:

       $obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, 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

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

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

	   When used as a function, like

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

	   or

	      require UNIVERSAL ;
	      $yes = UNIVERSAL::isa $a, "ARRAY";

	   , "isa" returns true in the same cases as above and also if "VAL" is an unblessed reference to a perl variable of type "TYPE", such as
	   "HASH", "ARRAY", or "Regexp".

       $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD )
	   "can" checks if the object or class has a method called "METHOD". If it does then a reference to the sub is returned. If it does not
	   then undef is returned.  This includes methods inherited or imported by $obj, "CLASS", or "VAL".

	   "can" cannot know whether an object will be able to provide a method through AUTOLOAD, so a return value of 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 perl-
	   sub) for methods they will handle via AUTOLOAD. For such 'dummy' subs, "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.

	   "can" can be called as a class (static) method, an object method, or a function.

	   When used as a function, if "VAL" is a blessed reference or package name which has a method called "METHOD", "can" returns a reference
	   to the subroutine.  If "VAL" is not a blessed reference, or if it does not have a method "METHOD", undef is returned.

       VERSION ( [ REQUIRE ] )
	   "VERSION" will return the value of the variable $VERSION in the package the object is blessed into. If "REQUIRE" is given then it will
	   do a comparison and die if the package version is not greater than or equal to "REQUIRE".

	   "VERSION" can be called as either a class (static) method, an object method or or a function.

       These subroutines should not be imported via "use UNIVERSAL qw(...)".  If you want simple local access to them you can do

	 *isa = &UNIVERSAL::isa;

       to import isa into your package.

perl v5.8.0							    2002-06-01							    UNIVERSAL(3pm)