package UNIVERSAL; our $VERSION = '1.00'; # UNIVERSAL should not contain any extra subs/methods beyond those # that it exists to define. The use of Exporter below is a historical # accident that can't be fixed without breaking code. Note that we # *don't* set @ISA here, don't want all classes/objects inheriting from # Exporter. It's bad enough that all classes have a import() method # whenever UNIVERSAL.pm is loaded. require Exporter; *import = \&Exporter::import; @EXPORT_OK = qw(isa can VERSION); 1; __END__ =head1 NAME UNIVERSAL - base class for ALL classes (blessed references) =head1 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 ; =head1 DESCRIPTION C is the base class which all bless references will inherit from, see L. C provides the following methods and functions: =over 4 =item $obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, TYPE ) C is a package name $obj is a blessed reference or a string containing a package name C is a package name C is any of the above or an unblessed reference When used as an instance or class method (C<$obj->isa( TYPE )>), C returns I if $obj is blessed into package C or inherits from package C. When used as a class method (Cisa( TYPE )>; sometimes referred to as a static method), C returns I if C inherits from (or is itself) the name of the package C or inherits from package C. 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"; , C returns I in the same cases as above and also if C is an unblessed reference to a perl variable of type C, such as "HASH", "ARRAY", or "Regexp". =item $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD ) C checks if the object or class has a method called C. If it does then a reference to the sub is returned. If it does not then I is returned. This includes methods inherited or imported by C<$obj>, C, or C. C cannot know whether an object will be able to provide a method through AUTOLOAD, so a return value of I 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 L) for methods they will handle via AUTOLOAD. For such 'dummy' subs, C 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. C can be called as a class (static) method, an object method, or a function. When used as a function, if C is a blessed reference or package name which has a method called C, C returns a reference to the subroutine. If C is not a blessed reference, or if it does not have a method C, I is returned. =item VERSION ( [ REQUIRE ] ) C will return the value of the variable C<$VERSION> in the package the object is blessed into. If C is given then it will do a comparison and die if the package version is not greater than or equal to C. C can be called as either a class (static) method, an object method or or a function. =back These subroutines should I be imported via S>. If you want simple local access to them you can do *isa = \&UNIVERSAL::isa; to import isa into your package. =cut