Enum EntryOrPlaceholder 

pub enum EntryOrPlaceholder<Key, Val, Plh, T> {
    Kept(T),
    Removed(Key, Val),
    Replaced(Plh, Val),
    ExistingPlaceholder(Plh),
    NewPlaceholder(Plh),
}

Result of an entry-or-placeholder operation at the shard level.

Variants

Kept(T)

Callback returned Retain(T) — entry is still in the cache.

Removed(Key, Val)

Callback returned Remove — entry was removed.

Replaced(Plh, Val)

Callback returned ReplaceWithGuard — entry was replaced with a placeholder. The old value is returned so it can be dropped outside the lock.

ExistingPlaceholder(Plh)

Found an existing placeholder (another loader is working on this key).

NewPlaceholder(Plh)

No entry existed, a new placeholder was created.