Deriving Traits

#[derive(...)] asks the compiler to auto-implement standard traits for structs and enums with correct field-wise logic.

Recipe

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct UserId(u64);
 
#[derive(Debug, serde::Serialize, serde::Deserialize)]
struct User {
    id: UserId,
    name: String,
}

When to reach for this: Rapid impl of Debug, Clone, equality, ordering, and serde when field semantics match derived behavior.

Working Example

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
enum Priority { Low, Medium, High }
 
fn main() {
    use std::collections::BTreeSet;
    let mut set = BTreeSet::new();
    set.insert(Priority::High);
    set.insert(Priority::Low);
    println!("{:?}", set);
}

What this demonstrates:

• Ord derive on enums requires discriminant ordering
• Hash + Eq enable HashSet/HashMap keys
• Copy added when all fields Copy
• Custom traits still need manual impl

Deep Dive

Common Derives

#[derive(Default)]

Picks first variant for enums or requires #[default] attribute on chosen variant (Rust 1.62+).

Cannot Derive

Display, Drop, From for arbitrary logic - manual impl or separate crates (thiserror, strum).

Gotchas

• Derive Eq on floats - Impossible. Fix: Use integers or partial_cmp manually.
• Derive Ord on floats - Not total order. Fix: Manual impl with partial_cmp wrapper type.
• Large Clone cost hidden - Derive clones all fields. Fix: Use Arc inside or avoid Clone.
• Derived Hash changes with field order - Reordering fields changes hash (same type). Fix: Stable schema versioning for persisted hashes.
• Conflicting manual + derive - Cannot both. Fix: Remove derive for that trait.

Alternatives

FAQs

Related

• Common Standard Traits
• Traits Basics
• thiserror
• Formatting & Printing

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.