UNIVERSAL - base class for ALL classes (blessed references)
$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 ;
UNIVERSAL is the base class which all bless references will inherit from,
UNIVERSAL provides the following methods and functions:
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 reference
When used as an instance or class method (
$obj-isa( TYPE )>),
returns true if $obj is blessed into package
TYPE or inherits from
When used as a class method (
CLASS-isa( TYPE )>; sometimes referred to as a
isa returns true if
CLASS inherits from (or is itself)
the name of the package
TYPE or inherits from package
When used as a function, like
use UNIVERSAL qw( isa ) ; $yes = isa $h, "HASH"; $yes = isa "Foo", "Bar";
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".
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
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,
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
When used as a function, if
VAL is a blessed reference or package name which
has a method called
can returns a reference to the subroutine.
VAL is not a blessed reference, or if it does not have a method
METHOD, undef is returned.
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
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 UNIVERSAL qw(...).
If you want simple local access to them you can do
*isa = \&UNIVERSAL::isa;
to import isa into your package.