How do I determine if an object implements a method in Perl?

Question

I've got a polymorphic array of objects which implement two (informal) interfaces. I want to be able to differentiate them with reflection along the lines of:

if (hasattr(obj, 'some_method')) {
    # `some_method` is only implemented by one interface.
    # Now I can use the appropriate dispatch semantics.
} else {
    # This must be the other interface.
    # Use the alternative dispatch semantics.
}

Maybe something like this works?:

if (*ref(obj)::'some_method') {
    # ...

I have difficulty telling when the syntax will try to invoke a subroutine and when it will return a subroutine reference. I'm not too familiar with package symbol tables ATM and I'm just trying to hack something out. :-)

Thanks in advance!

Answer 1

use Scalar::Util qw(blessed);
if( blessed($obj) and $obj->can('some_method') ){ 

}

"can" here is a method inherited by all classes from UNIVERSAL . Classes can override this method, but its not a good idea to.

Also, "can" returns a reference to the function, so you can do:

$foo->can('some_method')->( $foo , @args );

or

my $sub = $foo->can('some_method'); 
$foo->$sub( @args );

• Scalar::Util on search.CPAN.org
• Scalar::Util on perldoc.perl.org
• Perl Objects on perldoc.perl.org

Edit Updated Chain Syntax, thanks to Brian Phillips

Answer 2

Note that UNIVERSAL::can is not aware of AUTOLOAD methods. Here is a thread that discusses this in depth. See also UNIVERSAL::canAUTOLOAD and Class::AutoloadCAN.