A cache that holds a limited number of key-value pairs. When the capacity of the cache is exceeded, the least-recently-used (where "used" means a look-up or putting the pair into the cache) pair is automatically removed.
Contrary to the lru-cache crate (which
this crate is heavily inspired by!), the capacity is not the number of items
in the cache, but can be given by an arbitrary criterion by implementing
[Weighable
] for the value type V. A straight-forward example of this would
be to use the allocated size of the object, and provide a total capacity
which must not be exceeded by the cache.
use weight_cache::{Weighable, WeightCache};
use std::num::NonZeroUsize;
#[derive(PartialEq, Debug)]
enum Food {
Milk { milliliters: usize },
Cucumber { pieces: usize },
Meat { grams: usize },
Potato { pieces: usize },
Crab { grams: usize },
}
impl Weighable for Food {
fn measure(value: &Self) -> usize {
match value {
Food::Milk { milliliters } => milliliters * 104 / 100,
Food::Cucumber { pieces } => pieces * 158,
Food::Meat { grams } => *grams,
Food::Potato { pieces } => pieces * 175,
Food::Crab { grams } => *grams,
}
}
}
let mut cache = WeightCache::new(NonZeroUsize::new(500).unwrap());
// Can't put too much in!
assert!(cache.put(0, Food::Meat { grams: 600 }).is_err());
assert!(cache.is_empty());
cache.put(1, Food::Milk { milliliters: 100 }).unwrap();
assert!(!cache.is_empty());
assert_eq!(*cache.get(&1).unwrap(), Food::Milk { milliliters: 100 });
cache.put(2, Food::Crab { grams: 300 }).unwrap();
assert_eq!(*cache.get(&2).unwrap(), Food::Crab { grams: 300 });
assert_eq!(*cache.get(&1).unwrap(), Food::Milk { milliliters: 100 });
cache.put(3, Food::Potato { pieces: 2 }).unwrap();
assert_eq!(*cache.get(&3).unwrap(), Food::Potato { pieces: 2});
assert!(cache.get(&2).is_none()); // 1 has been touched last
assert_eq!(*cache.get(&1).unwrap(), Food::Milk { milliliters: 100 });
metrics
: Enables metric gathering on the cache. Register a [prometheus::Registry
] with a call to [WeightCache::register
]; set a custom metric namespace with [WeightCache::new_with_namespace
]
License: MIT OR Apache-2.0