I’ve recently added a function to my Blocks library that allows you to slugify any string.

What is a slug

A slug is the part of a URL that identifies a specific page on a website in a readable and concise way. For example, in the URL www.example.com/about-us, the slug is “about-us.”

Slugs have various other uses: you can use them to create file names in your file system, as Git branch names for issues you’re working on, and more.

What we need

Essentials. Slugs should only contain [a-z0-9-] characters ie no spaces, tabs, or underscores. Just letters, digits, and hyphens.

Accents removal. We want to remove accents from languages that use the Latin alphabet. This means characters like è, é, ê, ë, ě, ẽ, ē, ė, and ę should all be transformed to e.

Support for more alphabets. Strings written in alphabets other than Latin should be romanized as accurately as possible.

Basic emoji support. Emojis should be removed from the slug, except when the string consists solely of emojis.

We aim to achieve this without relying on external dependencies. Just Swift and Foundation.

The magic of applyingTransform

The StringProtocol protocol provides a powerful function called applyingTransform that performs most of these transformations. By applying a series of transformations, you can create an effective slugify function. The ones I used include:

  • .toLatin: Transliterates a string from any script to the Latin script;
  • .stripDiacritics: Removes diacritics from a string;
  • .stripCombiningMarks: Removes combining marks from a string;
  • .toUnicodeName: Converts characters to their Unicode names.

Examples

Here are some examples of what .slugify() does:

  • Hello Luka Dončić → hello-luka-doncic
  • 😀 LOL → lol
  • 😀 → grinning-face
  • 🎸 → guitar
  • สวัสดีชาวโลก → swasdi-chaw-lok (Thai for “Hello World”)

The code

You can check out an up-to-date version of slugify on GitHub.

Here’s the current implementation:

public extension StringProtocol {
    func slugify() -> String {
        var slug = lowercased()

        slug = slug.applyingTransform(.toLatin, reverse: false) ?? slug
        slug = slug.applyingTransform(.stripDiacritics, reverse: false) ?? slug
        slug = slug.applyingTransform(.stripCombiningMarks, reverse: false) ?? slug
        slug = slug.replacingOccurrences(of: "[^a-z0-9]+", with: "-", options: .regularExpression)
        slug = slug.trimmingCharacters(in: CharacterSet(charactersIn: "-"))

        if !isEmpty, slug.isEmpty {
            if let extendedSelf = applyingTransform(.toUnicodeName, reverse: false)?
                .replacingOccurrences(of: "\\N", with: ""), self != extendedSelf {
                return extendedSelf.slugify()
            }
        }

        return slug
    }
}