String extension to transform string into several case types

String+CaseTransform.swift

import Foundation

extension String {

    public var upperCasedFirstLetter: String {
        prefix(1).uppercased() + dropFirst()
    }

    public var lowerCasedFirstLetter: String {
        prefix(1).lowercased() + dropFirst()
    }

    public func lowerCamelCased() -> String {
        upperCamelCased().lowerCasedFirstLetter
    }

    public func upperCamelCased() -> String {
        let lowerCasedSelf = lowercased()
        let components = lowerCasedSelf.components(separatedBy: CharacterSet(charactersIn: " _-."))
        return components.reduce("") { partialResult, word in
            partialResult + word.capitalized
        }
    }

    public func camelCaseToSnakeCase() -> String {
        let components = componentsSeparatedByUppercase()
        return components.map({$0.lowercased()}).joined(separator: "_")
    }

    public func camelCaseToDotCase() -> String {
        let components = componentsSeparatedByUppercase()
        return components.map({$0.lowercased()}).joined(separator: ".")
    }

    private func componentsSeparatedByUppercase() -> [String] {
        var components: [String] = []
        var currentComponent = ""

        unicodeScalars.forEach { character in
            if currentComponent.isEmpty.not && character.caseType == CharacterCase.upper {
                components.append(currentComponent)
                currentComponent = character.escaped(asASCII: false)
            } else {
                currentComponent += character.escaped(asASCII: false)
            }
        }
        components.append(currentComponent)
        
        return components
    }
}

private enum CharacterCase {
    case lower
    case upper
    case none
}

extension UnicodeScalar {
    fileprivate var caseType: CharacterCase {
        if CharacterSet.lowercaseLetters.contains(self) { .lower }
        else if CharacterSet.uppercaseLetters.contains(self) { .upper }
        else { .none }
    }
}

extension Bool {
    fileprivate var not: Bool { !self }
}


// MARK: - Tests - 
// TODO: Move to a Test target

@testable import MyApp

import XCTest

final class StringCaseTransformTests: XCTestCase {

    func testLowerCamelCased() {
        let snakecaseString = "This_iS-a_string"
        let lowerCamelCased = snakecaseString.lowerCamelCased()

        XCTAssertEqual(lowerCamelCased, "thisIsAString")
    }

    func testUpperCamelCased() {
        let snakecaseString = "This_iS-a_string"
        let upperCamelCased = snakecaseString.upperCamelCased()

        XCTAssertEqual(upperCamelCased, "ThisIsAString")
    }

    func testCamelCaseToSnakeCase() {
        let camelcaseString = "thisIsAString"
        let snakecaseString = camelcaseString.camelCaseToSnakeCase()

        XCTAssertEqual(snakecaseString, "this_is_a_string")
    }

    func testCamelCaseToDotCase() {
        let camelcaseString = "thisIsAString"
        let dotcaseString = camelcaseString.camelCaseToDotCase()

        XCTAssertEqual(dotcaseString, "this.is.a.string")
    }
}