Convert Swift strings to camel case

Camelizer.swift

fileprivate let badChars = CharacterSet.alphanumerics.inverted

extension String {
    var uppercasingFirst: String {
        return prefix(1).uppercased() + dropFirst()
    }

    var lowercasingFirst: String {
        return prefix(1).lowercased() + dropFirst()
    }

    var camelized: String {
        guard !isEmpty else {
            return ""
        }

        let parts = self.components(separatedBy: badChars)

        let first = String(describing: parts.first!).lowercasingFirst
        let rest = parts.dropFirst().map({String($0).uppercasingFirst})

        return ([first] + rest).joined(separator: "")
    }
}

how did you come up with this? i am learning swift a while now and i am not gaining much knowledge.