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RedHat 9 (Linux i386) - man page for universal (redhat section 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 ref-
	   erence 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 declara-
	   tion (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 pack-
	   age 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)


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