There are different ways of representing a type of file, two popular ones being file extensions and another being Uniform Type Identifiers (UTIs) from the UIKit APIs. When working with a UIKit API such as UIDocumentPickerViewController we may need to distinguish between these types.

We can create independent types to hold file extensions and type identifiers, this makes it really clear which one is required for a particular piece of functionality. 👍

struct FileExtension {
    let rawValue: String

    func asTypeIdentifier() -> TypeIdentifier {
        let identifierCreated = UTTypeCreatePreferredIdentifierForTag(
            kUTTagClassFilenameExtension, rawValue as NSString, nil
        )
        if let typeIdentifier = identifierCreated?.takeRetainedValue() {
            return TypeIdentifier(rawValue: typeIdentifier as String)
        }
        return TypeIdentifier(rawValue: "public.data")
    }
}

struct TypeIdentifier {
    let rawValue: String
}

Thanks for reading and happy coding! 🙏