Macro local_cache

pub macro local_cache($request:expr, $v:expr $(,)?) {
    ...
}

Store and immediately retrieve a vector-like value $v (String or Vec<T>) in $request’s local cache using a locally generated anonymous type to avoid type conflicts.

Unlike local_cache_once, this macro’s generated code always returns a unique reference to request-local cache.

Note

The value $v must be of type String or Vec<T>, that is, a type that implements the sealed trait Shareablebb).

Example

use rocket::request::{local_cache, local_cache_once};

// The first store into local cache for a given type wins.
for i in 0..4 {
    assert_eq!(request.local_cache(|| i.to_string()), "0");
}

// This shows that we cannot cache different values of the same type; we
// _must_ use a proxy type. To avoid the need to write these manually, use
// `local_cache!`, which generates one of the fly.
for i in 0..4 {
    assert_eq!(local_cache!(request, i.to_string()), i.to_string());
}

// Note that while `local_cache_once!` generates a new type for the
// _macro_ invocation, that type is the same per run-time invocation, so
// all "calls" to `local_cache_once!` on the same line return the same
// reference for a given request.
for i in 1..4 {
    // Note that this is `1`, so _not_ the `String` from line 4.
    assert_eq!(local_cache_once!(request, i.to_string()), "1");
}