UNIVERSAL - base class for ALL classes

- 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 the perlobj manpage.

`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 the perlsub manpage) 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.

UNIVERSAL - base class for ALL classes