Adding slugification and style-based tags to SwiftUI
Aug 19, 2022 swiftuiopen-sourcetagging

As I’m currently rewriting my old Wally app from scratch for iOS 16 and SwiftUI 4, I’m adding a bunch of user requested features. One such feature is tagging, which will let users categorize their content. For reusability and sharing purposes, I’ve put all this tag-specific logic in a brand new, tiny package called TagKit. Let’s take a look!

TagKit logotype

Tagging is used in many platforms and applications, and I’m happy to finally add it to Wally. Since I will probably add this to other apps, I decided to extract tag-related functionality from Wally and libraries like SwiftKit and SwiftUIKit, which is part of my long-term strategy to make these large libraries smaller, in favor for smaller and more focused libraries. If this can also help others out, that’s a great bonus!

You probably don’t need an introduction to tagging, but let’s at least start with looking at slugifying strings, which is the process of converting string by removing unsupported characters and replacing whitespace with a separator.

Slugifying strings

You can see slugified strings in action in many web urls (for instance this one), where the page date and title is often slugified to create a unique valid url that also describes the content.

I wrote about slugifying strings in this blog post earlier this year. I use the same logic in TagKit, but made it a little more configurable.

In TagKit, the Slugifiable protocol describes a slugifyable type:

public protocol Slugifiable {

    var slugifiableValue: String { get }

String implements this protocol by default, by returning itself as the slugifiable value.

Once a type implements Slugifiable, it can be slugified with the slugified() function:

let string = "Hello, world!"
let slug = string.slugified() // Returns "hello-world"

You can also provide a custom SlugConfiguration to customize the slugified result:

let string = "Hello, world!"
let config = SlugConfiguration(
    separator: "+",
    allowedCharacters: NSCharacterSet(charactersIn: "hewo")
let slug = string.slugified(configuration: config) // Returns "he+wo"

You probably won’t need to use these functions directly, nor customize the configuration, but if you have to, you can.

Taggable types

With slugified strings in place, we can start looking at tagging, which is the process of adding tags (or labels) to items, which can be used to group, filter etc.

In TagKit, the Taggable protocol describes a taggable type:

public protocol Taggable {

    var tags: [String] { get set }

Once a type implements Taggable, it can make use of all the functionality that the protocol provides, such as hasTags, slugifiedTags, hasTag(...), addTag(...), removeTag(...), toggleTag(...) etc. Collections that contain Taggable types also get some additional functionality as well.

This means that you can now let your domain model types implement Taggable and automatically get access to a bunch of logic. This is also true for your observable SwiftUI view models, which means that you can easily create a UI where you can add, remove and toggle tags on an observable type, then write the changes back to the item that you are adding.


TagKit also has a few views that aim at making it easier to work with tags. For instance, TagList and TagEditList let you list and edit tags with a customizable tag view, TagCapsule renders tags with a customizable style and TagTextField automatically slugifies text as you type.

You can play around with previews in the TagView package, but a very basic example can look like this.

An animated gif of an app that uses TagKit

The demo above shows very plain tag capsules, but you can style these capsules in any way you like, or even replace them with your own custom views.


TagKit is currently a tiny library, but I really like how creating these small, super-focused packages makes it easy to reuse functionality and share what you create with the world.

Feel free to give the GitHub repository a try. I’m very interested in hearing what you think.