Introducing SelectiveEquatable

A few weeks ago, I released a blog post named “Selective Equality Checking in Swift”. In that post, I designed and implemented an API to check for equality on specific properties of a type. Today, I am excited to announce a new Swift protocol named SelectiveEquatable, that makes all of this even easier. Let’s see it in action.

Using SelectiveEquatable

To use the SelectiveEquatable protocol, all you need to do is add a conformance to it like this:

extension MySwiftType: SelectiveEquatable {}

And that’s it! Now you get a new method which allows you to check for equality on specific properties of your type.

let instance1 = MySwiftType(int: 1, string: "Hello", bool: true)
let instance2 = MySwiftType(int: 1, string: "World", bool: true)
print(instance1 == instance2) // false
print(instance1.isEqual(to: instance2, by: \.int, \.bool)) // true

Here we simply use the new isEqual(to:by:) method. We supply it a keypath to the properties we want to check for equality on. In this case, we are checking for equality on the int and bool properties. The by parameter will accept as many keypaths as you want, and for any type, as long as the type conforms to Equatable.

Installing SelectiveEquatable

There are two main ways to install SelectiveEquatable in your project. The first is to simply copy and paste the protocol into your project. You can find the entire code right here.

The second is to use the Swift Package Manager. If you already have a library that other code depends on, then it might be easier/more convenient to add the “SelectiveEquatable” package as a dependency to your project or package. The best place to find the package is on Swift Package Index!

Conclusion

I hope you find the SelectiveEquatable protocol useful in your projects. It is a simple and easy way to check for equality on specific properties of a type. Please star it on GitHub if you like it, and feel free to open an issue or pull request if you have any suggestions or improvements.