An Incoherent Rust
9 hours ago
- #Coherence
- #Rust
- #Ecosystem
- The Rust ecosystem faces challenges with foundational crates like serde, where implementing traits for types is required across the ecosystem, making it difficult to introduce alternatives.
- Coherence and orphan rules in Rust enforce that a trait can only be implemented once for a type, preventing overlapping implementations and ensuring soundness.
- Existing proposals to relax coherence and orphan rules, such as binary crate exemption, deferred coherence, and specialization, have limitations and don't fully solve ecosystem evolution problems.
- A radical proposal suggests removing coherence by introducing named impls and trait bound parameters, allowing for overlapping implementations while maintaining soundness.
- This approach could enable incoherent traits, where traits can have multiple implementations for the same type, addressing ecosystem evolution challenges.
- The proposal also explores implications for soundness, the HashMap problem, and how trait bounds on types versus impls differ in this model.
- Potential benefits include solving lifetime-dependent specialization, improving type system soundness, and enabling new language features like effect systems.
- The transition to this model would require significant compiler changes and language design work, including syntax for named impls and migration strategies.