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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 )
	  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 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.

Index for Section 3

Alphabetical listing for U

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