protocol OptionalMarkerProtocol {
    var orNil: String { get }
}

extension Optional: OptionalMarkerProtocol {
    var orNil : String {
        guard let me = self else {
            return "nil"
        }
        return "\(me)"
    }
}

func pretty1<T: Equatable>(_ value: T) -> String {
    let svalue: String
    if let optional = value as? OptionalMarkerProtocol {
        svalue = optional.orNil
    }
    else {
        svalue = String(describing: value)
    }
    
    return svalue
}

func pretty2(_ value: Any) -> String {
    let svalue: String
    if let optional = value as? OptionalMarkerProtocol {
        svalue = optional.orNil
    }
    else {
        svalue = String(describing: value)
    }
    
    return svalue
}

        let io: Int? = 10
        print(pretty1(io))
        print(pretty2(io as Any))