man UNIVERSAL () - base class for ALL classes (blessed references)

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

CWUNIVERSAL is the base class which all bless references will inherit from, see perlobj.

CWUNIVERSAL provides the following methods and functions: Where is a package name is a blessed reference or a string containing a package name is a package name is any of the above or an unblessed reference When used as an instance or class method (CW$obj->isa( TYPE )), CWisa returns true if CW$obj is blessed into package CWTYPE or inherits from package CWTYPE. When used as a class method (CWCLASS->isa( TYPE ): sometimes referred to as a static method), CWisa returns true if CWCLASS inherits from (or is itself) the name of the package CWTYPE or inherits from package CWTYPE. When used as a function, like 

   use UNIVERSAL qw( isa ) ;
   $yes = isa $h, "HASH";
   $yes = isa "Foo", "Bar";
or 
   require UNIVERSAL ;
   $yes = UNIVERSAL::isa $a, "ARRAY";
CWisa returns true in the same cases as above and also if CWVAL is an unblessed reference to a perl variable of type CWTYPE, such as HASH, ARRAY, or Regexp. CWcan checks if the object or class has a method called CWMETHOD. If it does then a reference to the sub is returned. If it does not then undef is returned. This includes methods inherited or imported by CW$obj, CWCLASS, or CWVAL. CWcan 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, CWcan 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. CWcan can be called as a class (static) method, an object method, or a function. When used as a function, if CWVAL is a blessed reference or package name which has a method called CWMETHOD, CWcan returns a reference to the subroutine. If CWVAL is not a blessed reference, or if it does not have a method CWMETHOD, undef is returned. CWVERSION will return the value of the variable CW$VERSION in the package the object is blessed into. If CWREQUIRE is given then it will do a comparison and die if the package version is not greater than or equal to CWREQUIRE. CWVERSION 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 (CWisa, CWcan, and CWVERSION), however it isn't usually necessary to do so. Perl magically makes these functions act as methods on all objects. The one exception is CWisa, which is useful as a function when operating on non-blessed references.