Enum AnyBackend 

#[non_exhaustive]
pub enum AnyBackend {
    Boxed(BoxedBackend),
}

Enum dispatch backend for eliminating vtable indirection on the hot path.

Enum Dispatch vs Vtable

This enum uses enum dispatch (also known as “inline dispatch”) to avoid vtable lookups for the built-in backends:

Approach	Pros	Cons
Enum dispatch (AnyBackend)	Zero-cost: no vtable indirection, better inlining, cache-friendly	Closed set of variants
Vtable (Box<dyn Backend>)	Open for extension, dynamic plugin loading	Virtual call overhead, harder to inline

Migration Path: Adding a New Backend (e.g., kqueue)

1. Create a new crate: kqueue/Cargo.toml
2. Implement the trait: impl Backend for KqueueBackend { ... }
3. Add the variant (optional, for zero-cost):

   // In core/src/backend.rs
   pub enum AnyBackend {
       Boxed(BoxedBackend),
       Kqueue(wireshift_kqueue::KqueueBackend), // Zero-cost variant
   }

4. Feature-flag it in the workspace Cargo.toml:

   [features]
   kqueue = ["dep:wireshift-kqueue"]

Send + Sync Guarantees

AnyBackend is Send + Sync because every variant contains only Send + Sync types. The compiler automatically derives these traits - no unsafe impl needed. If a future variant breaks this contract, the compiler will reject it.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Boxed(BoxedBackend)

A boxed backend (legacy or third-party).

Use this for foreign backends that aren’t part of the core wireshift workspace. For built-in backends, prefer dedicated variants for zero-cost dispatch.

Implementations

impl AnyBackend

pub fn from_boxed(backend: BoxedBackend) -> Self

Wrap a boxed backend into the enum dispatch.

Trait Implementations

impl Backend for AnyBackend

fn kind(&self) -> BackendKind

Returns the backend kind.

fn submit(&self, submission: BackendSubmission) -> Result<()>

Submits work to the backend.

fn cancel(&self, cancellation: CancellationHandle) -> Result<()>

Requests cancellation for in-flight work.

fn shutdown(&self) -> Result<()>

Shuts the backend down.