Pingora memory cache types

[RaoniSilvestre]

Just for context—I'm not an expert in Rust or memory caches, but I got curious about Pingora and was checking out its memory cache crate.

I noticed that the usual way to return data from the memory cache looks like this:

let cache: MemoryCache<i32, ()> = MemoryCache::new(10);
let (res, hit) = cache.get(&1);

Here, res is an Option, and hit is an enum that describes the cache state.

I was wondering—why return two separate values for this? Wouldn't something like this be simpler and more self-contained?

#[derive(Debug, PartialEq, Eq)]
/// [CacheStatus] indicates the response type for a query.
pub enum CacheStatus<T> {
    /// The key was found in the cache
    Hit(T),
    /// The key was not found.
    Miss,
    /// The key was found but it was expired.
    Expired,
    /// The key was not initially found but was found after awaiting a lock.
    LockHit,
    /// The returned value was expired but still returned. The [Duration] is
    /// how long it has been since its expiration time.
    Stale(T, Duration),
}

Just curious about the reasoning behind the design choice!