$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 $obj ;
"UNIVERSAL" provides the following methods and functions:
When used as an instance or class method ("$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";
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" 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" can be called as either a class (static) method, an object method or a function.
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.