Every Rust type should implement Debug, Send, Sync, Clone and Default

Common traits and their priority:

• Debug - every type should implement it
• Send and Sync - implement unless there is a specific reason not to. No Send means the type can’t be sent to another thread (no thread pools, no Mutex<T>). No Sync means a shared reference to the type can’t be sent across threads (no Arc<T> or static)
• Clone and Default - must implement
• PartialEq, PartialOrd, Hash, Eq and Ord - where possible implement them, especially PartialEq and PartialOrd
• Serialize and Deserialize - most libraries choose to provide a serde feature flag to not force a dependency

See also

• Principle of Least Astonishment - implementing standard traits is a Least Astonishment expectation
• &T Is a Shared Reference, Copy but Not Mutable - Sync is the thread-safety equivalent of &T. T is Sync if and only if &T is Send
• Interior Mutability Allows Mutation Through &T, Either by Runtime-Checked Exclusivity or In-Place Methods - types with interior mutability are not Sync because shared references could race
• Interface Segregation Principle (ISP) - the serde feature flag pattern is ISP applied to Rust crates: don’t force a serde dependency on callers who don’t need serialisation

References

• J. Gjengset, Rust for Rustaceans: Idiomatic Programming for Experienced Developers. No Starch Press, 2021.