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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 )"
      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, 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 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.

Index for Section 3

Alphabetical listing for U

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