UNIVERSAL - base class for ALL classes |
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,
see the perlobj manpage.
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 )>), 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''.
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
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
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.
UNIVERSAL - base class for ALL classes |