This manual page is for Mac OS X version 10.6.3

Reading manual pages

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 )"
           Where

           "TYPE"
               is a package name

           $obj
               is a blessed reference or a string containing a package name

           "CLASS"
               is a package name

           "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 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, call-ing calling
           ing 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 refer-ence, reference,
           ence, 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 a function.

EXPORTS
       None by default.

       You may request the import of all three functions ("isa", "can", and "VERSION"), however it isn't
       usually necessary to do so.  Perl magically makes these functions act as methods on all objects.  The
       one exception is "isa", which is useful as a function when operating on non-blessed references.



perl v5.8.9                                      2001-09-21                                   UNIVERSAL(3pm)