Hashable OptionSet in Swift

August 29, 2018 · 2 min read

This post explains how to create an OptionSet in Swift that also implements the Hashable protocol. That way it can be used in a Dictionary, for example. Even though it’s super simple, I couldn’t find a documented example online so I thought I’d put one together.

Motivation

I’ve been recently working on a game using Apple’s SpriteKit and reached a point where I needed to implement and track in-game achievements. A user on reddit suggested using an OptionSet to store which achievements have been unlocked and a Dictionary as an “achievements encyclopedia” of sorts, which turned out to be a great suggestion! In order to make that work, the OptionSet also had to implement the Hashable protocol.

Why it made sense for my use case:

Hashable Protocol Requirements

Final Code


This implementation uses the OptionSet’s rawValue as a unique indicator. Since hashValue defers to rawValue, it’s being used in the == function. This way we’re consolidating responsibility to hashValue. But alternatively you could:

return lhs.rawValue == rhs.rawValue

Using the OptionSet in a Dictionary


Resources

comments powered by Disqus