UUIDs are great, you can use them everywhere… but when you do so, it starts being hard to recognize where a UUID comes from.

A common pattern is to add readable prefixes to the UUIDs. This way, you can have user_ee505428-a17b-4935-b81c-266b81a63515 and post_d58a3f88-0493-458d-bd4b-a6ca4a2cc98c for example, making it easy to find which is which.

Writing this library, I wanted to keep it very simple and straight-forward. I also wanted the PrefixedUUIDs to be type-safe, meaning a UUID prefixed with user_ could not be used instead of a UUID prefixed by post_.

After writing PrefixedUUID, I realized prefixed UUIDs are just a subset of all the types we could want to prefix. That's why I made it more generic, by creating the Prefixed struct.

These are the features of PrefixedUUIDs, but you can say the same with any other prefixed type.

• Type safety: User.ID != Post.ID, even though they are stored the same way
• Codable: (Encodable & Decodable) conformance
• Practical: PrefixedUUIDs allow you to access the underlying UUID or the prefixed String, without storing anything more in memory or requiring expensive computations.
• Convenient: Foundation's UUID extensions make it easy to work with PrefixedUUIDs
• Type inference: Most of the time, you don't need to make associated types explicit
• Lightweight: PrefixedUUIDs take (almost) as little space in memory as UUIDs do. String prefixes are stored once ever and dashes in the UUID are not stored. The only thing that's stored for each PrefixedUUID is a UUID (which directly stores bytes).
• Case (in)sensitive: By default, prefixes are case sensitive, but with a simple option, you can choose for a prefix to be case insensitive.
• Debugging: Failing to decode a Prefixed type shows a human-readable error:
  • "'usr_abcdef' is not prefixed by 'user_'"
  • "'USR_MONPQR' is not prefixed by 'user_' (case insensitive)"
  • "user_ABCD" with a Prefixed Int => "'ABCD' is not a valid `Int`"
  • "user_56C68C54" with a Prefixed UUID => "'56C68C54' is not a valid `UUID`"

To use this package in a project, import the "prefixed-uuid" package like so:

dependencies: [
	// Other dependencies
	.package(
		name: "prefixed",
		url: "https://github.com/RemiBardon/swift-prefixed-type",
		.upToNextMajor(from: "2.0.0")
	),
],

Then add it to your target like so:

targets: [
	// ...
	.target(
		name: "<YourTarget>",
		dependencies: [
			// Other dependencies
			.product(name: "Prefixed", package: "prefixed"),
		]
	),
	// ...
]

To add Prefixed to your project, go to your project's configuration, then go to the Swift Packages tab, click + and follow XCode's instructions (Assuming you use XCode). When you're asked for a URL, enter https://github.com/RemiBardon/swift-prefixed-type.

The following uses PrefixedUUIDs, but you can use Prefixed<Prefix, Base> instead if you want.

First, create a type conforming to PrefixProtocol:

struct UserIDPrefix: PrefixProtocol {
	static var prefix: String { "user_" }
}

If you want the prefix to be case-insensitive, you can override the default (true) value:

struct CaseInsensitiveUserIDPrefix: PrefixProtocol {
	static var prefix: String { "lower_user_" }
	static var isCaseSensitive: Bool { false }
}

Then, use your new type as you would normally do:

struct User: Codable, Identifiable {
	typealias ID = PrefixedUUID<UserIDPrefix>
	let id: ID
}

Identifiable is not necessary, it's just here as a good practice. Codable is not necessary either, but you can use it: PrefixedUUID conforms to Codable.

There are many ways to create a PrefixedUUID:

• Using the verbose initializer:

  let prefixedUUID = PrefixedUUID<UserIDPrefix>(uuid: UUID())

• Using the default value (UUID()):

  let prefixedUUID = PrefixedUUID<UserIDPrefix>()

• Using the convenient UUID extensions:

  let prefixedUUID = UUID().prefixed(by: UserIDPrefix.self)

• The compiler can infer the type of your UUIDPrefix, so most of the time you just have to use .prefixed():

  let prefixedUUID: PrefixedUUID<UserIDPrefix> = UUID().prefixed()

• Do not make an existing struct conform to PrefixProtocol: PrefixProtocol sets custom String and debug descriptions which would override the one you expect.

• Package has been renamed from prefixed-uuid to prefixed
• Package library has been renamed from PrefixedUUID to Prefixed
• UUIDPrefix has been renamed to PrefixProtocol
  • UUIDPrefix.uuidPrefix has been renamed to PrefixProtocol.prefix
  • UUIDPrefix.uuidPrefixIsCaseSensitive has been renamed to PrefixProtocol.isCaseSensitive

As you would expect from a package this small, it is not actively developed. However, I still have a few things to add:

• Generic Prefixed struct, to be UUID-independent
• Swift documentation comments, to make the package more understandable
• Continuous Integration, to be sure the package runs in all environments
• Documentation page
• (Installation guides for older Swift Package Manager versions)
• (CONTRIBUTING guidelines)

This package is provided under MIT License. For more information, see LICENSE.