It's literally the whole thread man. Boxed nils are nils-but-also-not-nils, and knowing if something gets boxed means knowing whether the exact function paramet

It's literally the whole thread man. Boxed nils are nils-but-also-not-nils, and knowing if something gets boxed means knowing whether the exact function parameter signature (in or out) is an interface or concrete, not just whether what you are returning is of the appropriate type. (And Go has no special syntax for interface vs. concrete types in parameters, so you not only need to read the signature but the definition of the type.)