Type Alias HookFuture 

pub type HookFuture<'a> = Pin<Box<dyn Future<Output = Result<()>> + Send + 'a>>;

Future returned by pool lifecycle hooks.

Hooks are boxed rather than taking an AsyncFn because the hook future must be both Send (the pool is used from multi-threaded runtimes) and able to borrow the &AsyncConnection it is handed. On stable Rust those two requirements cannot be expressed together:

• Bounding an AsyncFn’s returned future as Send requires naming AsyncFnMut::CallRefFuture, which is behind unstable async_fn_traits.
• Return-type notation (F(&AsyncConnection): Send) is also unstable.
• A generic F: Fn(&'a AsyncConnection) -> Fut cannot work either, because Fut would have to depend on the higher-ranked lifetime 'a — the case that needs return-type notation or GATs.

So Box::pin(async move { .. }) at the call site is required, not merely conventional, and the examples on PoolConfig teach it deliberately. This matches the trait carve-out in upstream M-ASYNC-FN, which permits an explicit Future return “inside traits”. Revisit if async_fn_traits or return-type notation stabilizes.

Aliased Type

#[repr(transparent)]
pub struct HookFuture<'a> { /* private fields */ }