universal(3)
NAME
UNIVERSAL - base class for ALL classes (blessed refer
ences)
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
$obj is a blessed reference or a string containing - a package name
C<CLASS> is a package name
C<VAL> is any of the above or an unblessed refer - ence
- When used as an instance or class method ("$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 pack
age "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 refer
ence 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 $VER
SION 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 UNIVER
SAL qw(...)". If you want simple local access to them you
can do
*isa = UNIVERSAL::isa;- to import isa into your package.