Generics, Traits & Lifetimes

Generics, traits, and lifetimes are Rust’s compile-time abstraction toolkit: they remove duplication, state behavioral contracts, and prove borrowed data remains valid.

Concepts

• Generics
• Traits
• Trait Bounds
• Default Implementations
• Associated Types
• Generic Associated Types
• Lifetimes
• Lifetime Elision
• The ‘static Lifetime
• Where Clauses
• Blanket Implementations
• Marker Traits
• Supertraits
• Coherence and the Orphan Rule

Patterns

• Static Dispatch with Generics
• Use a Newtype to Implement Foreign Traits
• Sealed Traits

Antipatterns

• Overconstraining Lifetimes
• Unnecessary Bounds on Data Types
• Overgeneric Public APIs

Example

use std::fmt::Display;
 
fn announce_largest<'a, T>(left: &'a T, right: &'a T, label: impl Display) -> &'a T
where
    T: PartialOrd,
{
    println!("{label}");
    if left >= right { left } else { right }
}
 
fn main() {
    let a = 10;
    let b = 20;
    assert_eq!(*announce_largest(&a, &b, "numbers"), 20);
}

Reading Path

Start with Generics, Traits, and Lifetimes. Then read Trait Bounds, Where Clauses, and Lifetime Elision to understand signatures. Move to Associated Types, Generic Associated Types, and Blanket Implementations when designing reusable traits. Finish with Coherence and the Orphan Rule, Use a Newtype to Implement Foreign Traits, and Sealed Traits before publishing trait-heavy APIs.

See also

Ownership · Borrowing · References · The Iterator Trait · Dynamically Sized Types · Fully Qualified Syntax · Newtype Pattern · Zero-Cost Abstractions

Sources

• The Rust Programming Language, ch. 10 “Generic Types, Traits, and Lifetimes” — the-book, https://doc.rust-lang.org/book/ch10-00-generics.html
• The Rust Reference, “Generic parameters” — the-reference, https://doc.rust-lang.org/reference/items/generics.html
• The Rust Reference, “Traits” — the-reference, https://doc.rust-lang.org/reference/items/traits.html