enum_dispatch

enum_dispatch converts trait-object-style polymorphism (Box<dyn Trait>) into static enum-based dispatch, achieving up to 10x speedup by eliminating vtable lookups. Annotate a trait and enum with #[enum_dispatch], and it auto-generates match-based delegation plus From/TryInto conversions for each variant.

How it works

#[enum_dispatch]
trait Animal {
    fn name(&self) -> &str;
}

#[enum_dispatch(Animal)]
enum MyAnimal {
    Dog(Dog),
    Cat(Cat),
}

The macro generates a match arm for each variant, calling the trait method on the inner type directly. No heap allocation, no indirection, no vtable. It also enables serde serialization of "trait objects" — something impossible with dyn Trait.

Tradeoffs

• Same-crate constraint: trait and enum must be defined in the same crate
• Poor IDE support: rust-analyzer and RustRover struggle with the generated code
• No associated types: limited support for complex trait signatures

Alternatives

The right choice depends on your constraints: enum_dispatch for maximum performance in a single crate, ambassador for cross-crate generality, declarative_enum_dispatch when IDE support matters. See rust-enum-crates for the full dispatch landscape.