Lustre

An imperfect but more performant implementation of the Result pattern in Swift.

Lustre defines an interface with several manual specializations to improve compiler inference and and runtime performance over a Box<T>-based Result type, such as that from LlamaKit.

Day-to-day syntax of using Lustre's Result types are almost identical, except in that you must chose specific types to use for Result instances.

VoidResult and ObjectResult are fully-implemented specializations ready for use out of the box with no-return results and reference type results, respectively.

AnyResult is a fallback for any value type. Any is used as storage of any T. Types under 17 bytes in size will be stored inline, so results of all primitive types and most Swift collection types will have the same performance of a specialized generic enum. Larger types are stored using a native buffer type internal to Swift.

The CustomResult protocol exists for manual specializations for custom types of a known size. For example, a JSON-parsing library might provide a JSON enum, and JSONResult would conform to CustomResult with a .Success(JSON) case.

The common-case implementation of Result<T> is clearly the way forward. Until Swift supports multi-payload generic enums, Lustre.Result mitigates the performance problems around using a Box<T>-based Result type.

Availability

Lustre is intended for Swift 1.2. Compatibility with future versions is not guaranteed.

What's up with the name?

Result => Lustre. It's an anagram.