Of course, then there are people who advocate reversing this, and calling UNIVERSAL::isa($obj, "P") (does that count as a way to test for it?), and you can't stop that as far as I know.

Sure you can. UNIVERSAL::isa does just that to prevent people from breaking things like Test::MockObject.

In reply to Re^3: A class that cannot be subclassed. by chromatic
in thread A class that cannot be subclassed. by kyle

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