• NAME
• SYNOPSIS
• DESCRIPTION
• EXPORTS

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.