For the first case, I'd add an additional check:

    if(  ref($obj)  &&  UNIVERSAL::isa($obj,'Class')  ) {
        $obj->invoke_method();
    }
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since UNIVERSAL::isa("main",'main') returns true even though "main" is not an object; UNIVERSAL::isa() works on class names as well.

For your second test, I'd go a quite different route:     if(  ref($obj)  &&  UNIVERSAL::isa($obj,'UNIVERSAL')  ) { or, just to be shorter:

    if(  ref($obj)  &&  UNIVERSAL::can($obj,'can')  ) {
# or
    if(  ref($obj)  &&  UNIVERSAL::can($obj,'isa')  ) {
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You can also do:     use UNIVERSAL qw( isa can ); to make the above tests much shorter to write (allowing you to drop "UNIVERSAL::" in each).

This all partially illustrates why it was a mistake for ref() to deal with both reference nature and blessedness nature. ref() should only return things like 'ARRAY' while a separate function, blessed() should tell you whether the item is a blessed reference or not (and probably return the package into which it was blessed, though using such information directly is usually a bad idea).

        - tye (but my friends call me "Tye")