dreaded orphan rule
Yeah, that always struck me as stupid.
It is necessary to guarantee consistency in the trait system, otherwise it could lead to memory unsafety. Even relaxing it in cases where overlapping implementations could always be catched is still problematic because the compiler sometimes performs negative reasoning about traits that it know cannot be implemented downstream due to the the orphan rule.
And if you think about it the orphan rule is not worse than what other languages allow. For example C# only allow implementing an interface when defining a type, while the orphan rule also allows you to implement a trait when defining the trait itself. Not to mention being able to implement a trait only when a generic parameter implements another trait.
Yeah, the borrow checker is a bit too strict IMO. Ideally, the borrow checker would only trigger on things that could be run in parallel, such as with threads or async.
You can still trivially violate memory safety without multithreading or concurrency. The article touches on this a bit (they mention e.g. iterator invalidation) but they fail to address all issues.
https://manishearth.github.io/blog/2015/05/17/the-problem-with-shared-mutability/
the orphan rule is not worse than what other languages allow
Sure, but that doesn’t mean it can’t be better.
Surely the compiler could delay optimizations until the entire project is built, no? Then it knows what implementations exist, and the developer could then decide how to deal with that. Perhaps the dev could decorate the trait impl as overriding all others, overriding one specific impl, etc.
The orphan rule feels like throwing the baby out with the bathwater.
You can still trivially violate memory safety without multithreading or concurrency
Sure, and ideally those cases would be accounted for, or at the very least the dev could annotate each use to turn the borrow checker off for each instance, and that could print something at build time and a linter could flag over it. Unsafe blocks aren’t feasible for everything here.
A lot of these situations are fine in practice. Give devs the ability to sidestep the rules and take responsibility for the outcome.
