UNIVERSAL(3)

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 inher-
           its 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 neces-
           sarily mean the object will not be able to handle the method call.
           To get around this some module authors use a forward declaration
           (see perlsub) 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(3)