TextCaseStyle.swift

enum Style {
    case normal
    case uppercased
}

extension Style {
    func applyLetterCaseToText(_ text: String) -> String {
        switch self {
        case .normal:
            return text
        case .uppercased:
            return text.uppercased()
        }
    }
}

let text = "Lorem ipsum"
let style = Style.uppercased
let styledText = style.applyLetterCaseToText(text)

extension String {
    func applyingLetterCase(_ style: Style) -> String {
        return style.applyLetterCaseToText(self)
    }
}

let anotherStyledText = text.applyingLetterCase(.uppercased)