Architectural Cost of Rust's Orphan Rule

The architectural cost of Rust's orphan rule doesn't show up on day one. It shows up when you're six months deep into a monorepo, the domain model is clean, crate split looks sane — and then you try to wire two libraries together, and the compiler just says no. No negotiation, no workaround at the language level. Foreign types don't connect to foreign traits. That's the rule.

If you're coming from Java or C#, the instinct is to extend. OOP gives you ad-hoc polymorphism for free — bolt any interface onto any object, anywhere, anytime. Rust's coherence system exists specifically to make that impossible, and the collision between those two mental models is where experienced engineers lose days they don't budget for.