Swiftpack.co - Package - mz2/WeightedLRUCache

WeightedLRUCache Swift Package Manager compatible Build Status MIT License

An LRU cache in Swift, with optional support for weighted values such that values are evicted from the tail until a total weight parameter is satisfied.


Add WeightedLRUCache to your Swift package as a dependency by adding the following to your Package.swift file in the dependencies array:

.package(url: "https://github.com/mz2/WeightedLRUCache.git", from: "<version>")

If you are using Xcode 11 or newer, you can add CLIKit by entering the URL to the repository via the File menu:

File > Swift Packages > Add Package Dependency...


Values inserted into a WeightedLRUCache<Key, Value> must conform to the protocol Weighted (which simply requires a readonly property weight: UInt on the conforming type). An example implementation WeightedValue is provided with the library.

To create a cache with no constrained item count, and a max weight constraint of 10, do the following:

var cache = WeightedLRUCache<String, WeightedValue<String>>(maxCount: .max, maxWeight: 10) { key, value in
   print("Dropped \(key) : \(value)")

Note above the use of Int.max as the max count -- here only a weight constraint was given (both item count and total weight can be constrained). Let's add two more items in there:

cache["a"] = WeightedValue<String>(weight: 5, value: "foo")
cache["b"] = WeightedValue<String>(weight: 5, value: "bar")

// Upon this being inserted, value with key "a" above is dropped,
// and the callback passed to the cache initializer is called for the first inserted value.
cache["c"] = WeightedValue<String>(weight: 1, value: "baz")

A cache created as above behaves such that...

  • the first inserted value (with key "a") will be dropped after the next two have been inserted (since the 3rd insertion brings the total weight to 11, i.e. above the maximum of 10).
  • the callback passed into the initializer is called (synchronously, in the call stack that results from the cache insertion of key "c" below).

Beside a subscript based interface for key-based access, keys and values arrays available on WeightedLRUCache to return values in the order in which they were accessed by their key. Given the example above, keys for example returns the array ["c", "b", "a"].

For more usage examples, see the project's test suite.


WeightedLRUCache is available under the MIT license.


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