Not sure what you mean. Duck typing suffers from the false cognate problem, and mixins suffer from false cognates and potential collisions. They also do nothi

Not sure what you mean. Duck typing suffers from the false cognate problem, and mixins suffer from false cognates and potential collisions. They also do nothing to ensure type safety or optional type-based compile-time optimizations. More importantly, these features could also be trivially added in other languages as libraries. Non-Moose Perl 5, Tcl, Lisp-pre-CLOS, Lua, and JavaScript to some extent demonstrate the "you can roll your own object system trivially!" fallacy, especially when you want to use libraries written by other people. Likewise, I'm not aware of anyone who's used roles in a serious project who wants to go back to object systems without them.