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

    if(  ref($obj)  &&  UNIVERSAL::isa($obj,'Class')  ) {
        $obj->invoke_method();
    }
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For your second test, I'd go a quite different route:     if(  ref($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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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).

The second test you pose is probably the more efficient, but you overlook a few candidates:

    my $ref;
    if ($ref = ref($obj) and $ref !~ /^(SCALAR|ARRAY|HASH|GLOB|Regexp)
+$/) {
        $obj->method();
    }
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Technically, the Regexp references are objects, but they are part of the core, and wouldn't represent an application-defined class. Of course, you can drop that from the regex above, if you like.

--rjray

Efficiency is nice, but there's something to be said for correctness as well. You've also forgotten REF, CODE, and LVALUE.

Comparing the return value from ref to a list of known types is simply the wrong approach. Either you'll forget something, or a new type will be added in a future version and your code will break.

Go with the UNIVERSAL::isa() approach. Really.

I agree, but to clarify, the best approach would seem to be:

    if (ref($obj) and UNIVERSAL::isa($obj, 'UNIVERSAL')) {
        ...
    }
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Well, "best" in absence of the blessed primitive, of course...

--rjray