[lmm]

> What we’re doing is fine. You should get your serialization and I should get mine. But if either of us declares, process-wide, that one of us has determined the One True Serialization of PairOfInts, I think we are wrong.

Well, fine, but then you need to actually implement a module system or something. Currently trait impls are program-wide, and if you say that you're not allowed to make global impls of a trait then that's the same as saying you're not allowed to implement traits at all.

[amluto]

Rust’s orphan rule has the property that there is no spooky action at all distance in terms of program semantics. If I write a library, my library behaves the same way regardless of whether the main program imports a different library.

In any case, the OP’s proposed “incoherent” scheme actually is a module system of sorts for conflicting trait impls, and it seems about right for something like serialization.