I've actually been doing some experiments recently with signatures 0.09, and the results have been not great.
https://github.com/kraih/mojo/compare/signatures
Even if we only use a feature subset supported by both, the module and the core feature, there are still too many bugs to make it even somewhat workable. Biggest blocker was this one.
https://rt.cpan.org/Ticket/Display.html?id=80450
The prototype attribute being called :proto instead of :prototype was also surprisingly annoying, but easy to work around with Scalar::Util::set_prototype.
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sebastian