Errors occurring in switch statement

func weatherIconFromString(stringIcon: String) -> UIImage
{
    var imageName = String

    switch stringIcon {
    case "clear-day":
        imageName = "clear-day"
    case "clear-night":
        imageName = "clear-night"
    case "rain":
        imageName = "rain"
    case "snow":
        imageName = "snow"
    case "sleet":
        imageName = "sleet"
    case "wind":
        imageName = "wind"
    case "fog":
        imageName = "fog"
    case "cloudy":
        imageName = "cloudy"
    case "partly-cloudy-day":
        imageName = "partly-cloudy"
    case "partly-cloudy-night":
        imageName = "cloudy-night"
    default:
        imageName = "default"
    }

    var iconImage = UIImage(named: imageName)
    return iconImage
}