Struct RefKeyEntrySelector

pub struct RefKeyEntrySelector<'a, K, Q, V, S>
where
    Q: ?Sized,
{ /* private fields */ }

Provides advanced methods to select or insert an entry of the cache.

Many methods here return an Entry, a snapshot of a single key-value pair in the cache, carrying additional information like is_fresh.

RefKeyEntrySelector is constructed from the entry_by_ref method on the cache.

Implementations

impl<'a, K, Q, V, S> RefKeyEntrySelector<'a, K, Q, V, S>

where K: Borrow<Q> + Hash + Eq + Send + Sync + 'static, Q: ToOwned<Owned = K> + Hash + Eq + ?Sized, V: Clone + Send + Sync + 'static, S: BuildHasher + Clone + Send + Sync + 'static,

pub async fn and_compute_with<F, Fut>(self, f: F) -> CompResult<K, V>

where F: FnOnce(Option<Entry<K, V>>) -> Fut, Fut: Future<Output = Op<V>>,

Performs a compute operation on a cached entry by using the given closure f. A compute operation is either put, remove or no-operation (nop).

The closure f should take the current entry of Option<Entry<K, V>> for the key, and return a Future that resolves to an ops::compute::Op<V> enum.

This method works as the followings:

1. Apply the closure f to the current cached Entry, and get a Future.
2. Resolve the Future, and get an ops::compute::Op<V>.
3. Execute the op on the cache:
   • Op::Put(V): Put the new value V to the cache.
   • Op::Remove: Remove the current cached entry.
   • Op::Nop: Do nothing.
4. Return an ops::compute::CompResult<K, V> as the followings:

Op<V>	Entry<K, V> already exists?	CompResult<K, V>	Notes
Put(V)	no	Inserted(Entry<K, V>)	The new entry is returned.
Put(V)	yes	ReplacedWith(Entry<K, V>)	The new entry is returned.
Remove	no	StillNone(Arc<K>)
Remove	yes	Removed(Entry<K, V>)	The removed entry is returned.
Nop	no	StillNone(Arc<K>)
Nop	yes	Unchanged(Entry<K, V>)	The existing entry is returned.

See Also

• If you want the Future resolve to Result<Op<V>> instead of Op<V>, and modify entry only when resolved to Ok(V), use the and_try_compute_with method.
• If you only want to update or insert, use the and_upsert_with method.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12.8", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::{
    future::Cache,
    ops::compute::{CompResult, Op},
};

#[tokio::main]
async fn main() {
    let cache: Cache<String, u64> = Cache::new(100);
    let key = "key1";

    /// Increment a cached `u64` counter. If the counter is greater than or
    /// equal to 2, remove it.
    async fn inclement_or_remove_counter(
        cache: &Cache<String, u64>,
        key: &str,
    ) -> CompResult<String, u64> {
        cache
            .entry_by_ref(key)
            .and_compute_with(|maybe_entry| {
                let op = if let Some(entry) = maybe_entry {
                    let counter = entry.into_value();
                    if counter < 2 {
                        Op::Put(counter.saturating_add(1)) // Update
                    } else {
                        Op::Remove
                    }
                } else {
                      Op::Put(1) // Insert
                };
                // Return a Future that is resolved to `op` immediately.
                std::future::ready(op)
            })
            .await
    }

    // This should insert a now counter value 1 to the cache, and return the
    // value with the kind of the operation performed.
    let result = inclement_or_remove_counter(&cache, &key).await;
    let CompResult::Inserted(entry) = result else {
        panic!("`Inserted` should be returned: {result:?}");
    };
    assert_eq!(entry.into_value(), 1);

    // This should increment the cached counter value by 1.
    let result = inclement_or_remove_counter(&cache, &key).await;
    let CompResult::ReplacedWith(entry) = result else {
        panic!("`ReplacedWith` should be returned: {result:?}");
    };
    assert_eq!(entry.into_value(), 2);

    // This should remove the cached counter from the cache, and returns the
    // _removed_ value.
    let result = inclement_or_remove_counter(&cache, &key).await;
    let CompResult::Removed(entry) = result else {
        panic!("`Removed` should be returned: {result:?}");
    };
    assert_eq!(entry.into_value(), 2);

    // The key should no longer exist.
    assert!(!cache.contains_key(key));

    // This should start over; insert a new counter value 1 to the cache.
    let result = inclement_or_remove_counter(&cache, &key).await;
    let CompResult::Inserted(entry) = result else {
        panic!("`Inserted` should be returned: {result:?}");
    };
    assert_eq!(entry.into_value(), 1);
}

Concurrent calls on the same key

This method guarantees that concurrent calls on the same key are executed serially. That is, and_compute_with calls on the same key never run concurrently. The calls are serialized by the order of their invocation. It uses a key-level lock to achieve this.

pub async fn and_try_compute_with<F, Fut, E>( self, f: F, ) -> Result<CompResult<K, V>, E>

where F: FnOnce(Option<Entry<K, V>>) -> Fut, Fut: Future<Output = Result<Op<V>, E>>, E: Send + Sync + 'static,

Performs a compute operation on a cached entry by using the given closure f. A compute operation is either put, remove or no-operation (nop).

The closure f should take the current entry of Option<Entry<K, V>> for the key, and return a Future that resolves to a Result<ops::compute::Op<V>, E>.

This method works as the followings:

1. Apply the closure f to the current cached Entry, and get a Future.
2. Resolve the Future, and get a Result<ops::compute::Op<V>, E>.
3. If resolved to Err(E), return it.
4. Else, execute the op on the cache:
   • Ok(Op::Put(V)): Put the new value V to the cache.
   • Ok(Op::Remove): Remove the current cached entry.
   • Ok(Op::Nop): Do nothing.
5. Return an Ok(ops::compute::CompResult<K, V>) as the followings:

Op<V>	Entry<K, V> already exists?	CompResult<K, V>	Notes
Put(V)	no	Inserted(Entry<K, V>)	The new entry is returned.
Put(V)	yes	ReplacedWith(Entry<K, V>)	The new entry is returned.
Remove	no	StillNone(Arc<K>)
Remove	yes	Removed(Entry<K, V>)	The removed entry is returned.
Nop	no	StillNone(Arc<K>)
Nop	yes	Unchanged(Entry<K, V>)	The existing entry is returned.

See Also

• If you want the Future resolve to Op<V> instead of Result<Op<V>>, use the and_compute_with method.
• If you only want to update or insert, use the and_upsert_with method.

Example

See try_append_value_async.rs in the examples directory.

Concurrent calls on the same key

This method guarantees that concurrent calls on the same key are executed serially. That is, and_try_compute_with calls on the same key never run concurrently. The calls are serialized by the order of their invocation. It uses a key-level lock to achieve this.

pub async fn and_upsert_with<F, Fut>(self, f: F) -> Entry<K, V>

where F: FnOnce(Option<Entry<K, V>>) -> Fut, Fut: Future<Output = V>,

Performs an upsert of an Entry by using the given closure f. The word “upsert” here means “update” or “insert”.

The closure f should take the current entry of Option<Entry<K, V>> for the key, and return a Future that resolves to a new value V.

This method works as the followings:

1. Apply the closure f to the current cached Entry, and get a Future.
2. Resolve the Future, and get a new value V.
3. Upsert the new value to the cache.
4. Return the Entry having the upserted value.

See Also

• If you want to optionally upsert, that is to upsert only when certain conditions meet, use the and_compute_with method.
• If you try to upsert, that is to make the Future resolve to Result<V> instead of V, and upsert only when resolved to Ok(V), use the and_try_compute_with method.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12.8", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::future::Cache;

#[tokio::main]
async fn main() {
    let cache: Cache<String, u64> = Cache::new(100);
    let key = "key1";

    let entry = cache
        .entry_by_ref(key)
        .and_upsert_with(|maybe_entry| {
            let counter = if let Some(entry) = maybe_entry {
                entry.into_value().saturating_add(1) // Update
            } else {
                1 // Insert
            };
            // Return a Future that is resolved to `counter` immediately.
            std::future::ready(counter)
        })
        .await;
    // It was not an update.
    assert!(!entry.is_old_value_replaced());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), 1);

    let entry = cache
        .entry_by_ref(key)
        .and_upsert_with(|maybe_entry| {
            let counter = if let Some(entry) = maybe_entry {
                entry.into_value().saturating_add(1)
            } else {
                1
            };
            std::future::ready(counter)
        })
        .await;
    // It was an update.
    assert!(entry.is_old_value_replaced());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), 2);
}

Concurrent calls on the same key

This method guarantees that concurrent calls on the same key are executed serially. That is, and_upsert_with calls on the same key never run concurrently. The calls are serialized by the order of their invocation. It uses a key-level lock to achieve this.

pub async fn or_default(self) -> Entry<K, V>

where V: Default,

Returns the corresponding Entry for the reference of the key given when this entry selector was constructed. If the entry does not exist, inserts one by cloning the key and calling the default function of the value type V.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::future::Cache;

#[tokio::main]
async fn main() {
    let cache: Cache<String, Option<u32>> = Cache::new(100);
    let key = "key1".to_string();

    let entry = cache.entry_by_ref(&key).or_default().await;
    assert!(entry.is_fresh());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), None);

    let entry = cache.entry_by_ref(&key).or_default().await;
    // Not fresh because the value was already in the cache.
    assert!(!entry.is_fresh());
}

pub async fn or_insert(self, default: V) -> Entry<K, V>

Returns the corresponding Entry for the reference of the key given when this entry selector was constructed. If the entry does not exist, inserts one by cloning the key and using the given default value for V.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::future::Cache;

#[tokio::main]
async fn main() {
    let cache: Cache<String, u32> = Cache::new(100);
    let key = "key1".to_string();

    let entry = cache.entry_by_ref(&key).or_insert(3).await;
    assert!(entry.is_fresh());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), 3);

    let entry = cache.entry_by_ref(&key).or_insert(6).await;
    // Not fresh because the value was already in the cache.
    assert!(!entry.is_fresh());
    assert_eq!(entry.into_value(), 3);
}

pub async fn or_insert_with(self, init: impl Future<Output = V>) -> Entry<K, V>

Returns the corresponding Entry for the reference of the key given when this entry selector was constructed. If the entry does not exist, inserts one by cloning the key and resolving the init future for the value.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::future::Cache;

#[tokio::main]
async fn main() {
    let cache: Cache<String, String> = Cache::new(100);
    let key = "key1".to_string();

    let entry = cache
        .entry_by_ref(&key)
        .or_insert_with(async { "value1".to_string() })
        .await;
    assert!(entry.is_fresh());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), "value1");

    let entry = cache
        .entry_by_ref(&key)
        .or_insert_with(async { "value2".to_string() })
        .await;
    // Not fresh because the value was already in the cache.
    assert!(!entry.is_fresh());
    assert_eq!(entry.into_value(), "value1");
}

Concurrent calls on the same key

This method guarantees that concurrent calls on the same not-existing entry are coalesced into one evaluation of the init future. Only one of the calls evaluates its future (thus returned entry’s is_fresh method returns true), and other calls wait for that future to resolve (and their is_fresh return false).

For more detail about the coalescing behavior, see Cache::get_with.

pub async fn or_insert_with_if( self, init: impl Future<Output = V>, replace_if: impl FnMut(&V) -> bool + Send, ) -> Entry<K, V>

Works like or_insert_with, but takes an additional replace_if closure.

This method will resolve the init future and insert the output to the cache when:

• The key does not exist.
• Or, replace_if closure returns true.

pub async fn or_optionally_insert_with( self, init: impl Future<Output = Option<V>>, ) -> Option<Entry<K, V>>

Returns the corresponding Entry for the reference of the key given when this entry selector was constructed. If the entry does not exist, clones the key and resolves the init future. If Some(value) was returned by the future, inserts an entry with the value . If None was returned, this method does not insert an entry and returns None.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::future::Cache;

#[tokio::main]
async fn main() {
    let cache: Cache<String, u32> = Cache::new(100);
    let key = "key1".to_string();

    let none_entry = cache
        .entry_by_ref(&key)
        .or_optionally_insert_with(async { None })
        .await;
    assert!(none_entry.is_none());

    let some_entry = cache
        .entry_by_ref(&key)
        .or_optionally_insert_with(async { Some(3) })
        .await;
    assert!(some_entry.is_some());
    let entry = some_entry.unwrap();
    assert!(entry.is_fresh());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), 3);

    let some_entry = cache
        .entry_by_ref(&key)
        .or_optionally_insert_with(async { Some(6) })
        .await;
    let entry = some_entry.unwrap();
    // Not fresh because the value was already in the cache.
    assert!(!entry.is_fresh());
    assert_eq!(entry.into_value(), 3);
}

Concurrent calls on the same key

This method guarantees that concurrent calls on the same not-existing entry are coalesced into one evaluation of the init future. Only one of the calls evaluates its future (thus returned entry’s is_fresh method returns true), and other calls wait for that future to resolve (and their is_fresh return false).

For more detail about the coalescing behavior, see Cache::optionally_get_with.

pub async fn or_try_insert_with<F, E>( self, init: F, ) -> Result<Entry<K, V>, Arc<E>>

where F: Future<Output = Result<V, E>>, E: Send + Sync + 'static,

Returns the corresponding Entry for the reference of the key given when this entry selector was constructed. If the entry does not exist, clones the key and resolves the init future. If Ok(value) was returned from the future, inserts an entry with the value. If Err(_) was returned, this method does not insert an entry and returns the Err wrapped by std::sync::Arc.

Example

// Cargo.toml
//
// [dependencies]
// moka = { version = "0.12", features = ["future"] }
// tokio = { version = "1", features = ["rt-multi-thread", "macros" ] }

use moka::future::Cache;

#[tokio::main]
async fn main() {
    let cache: Cache<String, u32> = Cache::new(100);
    let key = "key1".to_string();

    let error_entry = cache
        .entry_by_ref(&key)
        .or_try_insert_with(async { Err("error") })
        .await;
    assert!(error_entry.is_err());

    let ok_entry = cache
        .entry_by_ref(&key)
        .or_try_insert_with(async { Ok::<u32, &str>(3) })
        .await;
    assert!(ok_entry.is_ok());
    let entry = ok_entry.unwrap();
    assert!(entry.is_fresh());
    assert_eq!(entry.key(), &key);
    assert_eq!(entry.into_value(), 3);

    let ok_entry = cache
        .entry_by_ref(&key)
        .or_try_insert_with(async { Ok::<u32, &str>(6) })
        .await;
    let entry = ok_entry.unwrap();
    // Not fresh because the value was already in the cache.
    assert!(!entry.is_fresh());
    assert_eq!(entry.into_value(), 3);
}

Concurrent calls on the same key

This method guarantees that concurrent calls on the same not-existing entry are coalesced into one evaluation of the init future (as long as these futures return the same error type). Only one of the calls evaluates its future (thus returned entry’s is_fresh method returns true), and other calls wait for that future to resolve (and their is_fresh return false).

For more detail about the coalescing behavior, see Cache::try_get_with.