Struct persisted::SingletonKey

pub struct SingletonKey<V> { /* private fields */ }

A persisted key for a value type that appears only once in a program. The name of the value type is the only information available as the key, hence why the value type must only be used once.

Example

use persisted::{Persisted, PersistedKey, PersistedStore, SingletonKey};

enum Foo {
    Bar,
    Baz,
}

#[derive(PersistedKey)]
#[persisted(Foo)]
struct FooKey;

// These two values are equivalent
let value1: Persisted<Store, _> =
    Persisted::new(SingletonKey::default(), Foo::Bar);
let value2: Persisted<Store, _> = Persisted::new(FooKey, Foo::Bar);


struct Store;

impl<K: PersistedKey> PersistedStore<K> for Store {
    fn load_persisted(key: &K) -> Option<K::Value> {
        None
    }
    fn store_persisted(key: &K, value: &K::Value) {}
}

Trait Implementations

impl<V: Clone> Clone for SingletonKey<V>

fn clone(&self) -> SingletonKey<V>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<V> Debug for SingletonKey<V>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<V> Default for SingletonKey<V>

fn default() -> Self

Returns the “default value” for a type.

impl<V> PersistedKey for SingletonKey<V>

type Value = V

The type of the persisted value associated with this key

fn type_name() -> &'static str

Get a unique name for this key type. This should be globally unique within the scope of your program. This is important to use while persisting because most serialization formats don’t include the name of the type, just the content. This unique name allows the store to disambiguate between different key types of the same structure, which is particular important for unit keys. For example, if your store persists data as JSON, a serialized key may be just an ID, e.g. 3. This alone is not a useful key because it’s ambiguous in the scope of your entire program. This method allows you to include the key type, so you could serialize the same key as ["Person", 3] or {"type": "Person", "key": 3}. It’s up to the PersistedStore implementation to decide how to actually employ this function, it’s provided merely as a utility.

impl<V: Copy> Copy for SingletonKey<V>