Use of local variable warning 'weatherImageFromIconString'

//start
import Foundation
import UIKit


enum Icon: String {
    case ClearDay = "clear-day"
    case ClearNight = "clear-night"
    case Rain = "rain"
    case Snow = "snow"
    case Sleet = "sleet"
    case Wind = "wind"
    case Fog = "fog"
    case Cloudy = "cloudy"
    case PartlyCloudyDay = "partly-cloudy-day"
    case PartlyCloudyNight = "partly-cloudy-night"
}


struct CurrentWeather {

    let temperature: Int?
    let humidity: Int?
    let precipProbability: Int?
    let summary: String?
    var icon: UIImage? = UIImage(named: "default.png")

    init(weatherDictionary: [String: AnyObject]) {
        temperature = weatherDictionary["temperature"] as? Int
        if let humidityFloat = weatherDictionary["humidity"] as? Double {

        humidity = Int(humidityFloat * 100)
        } else {
            humidity = nil
        }
        if let precipFloat = weatherDictionary["precipProbability"] as? Double {

        precipProbability = Int(precipFloat * 100)
        } else {
            precipProbability = nil
        }
        summary = weatherDictionary["summary"] as? String

        if let iconString = weatherDictionary["icon"] as? String {
            icon = weatherImageFromIconString(iconString)
        }

        func weatherImageFromIconString(iconString: String) -> UIImage? {
            var imageName: String

            if let iconValue = Icon(rawValue: iconString) {
                switch iconValue {
                case .ClearDay:
                    imageName = "clear-day.png"
                case .ClearNight:
                    imageName = "clear-night.png"
                case .Rain:
                    imageName = "rain.png"
                case .Snow:
                    imageName = "snow.png"
                case .Sleet:
                    imageName = "sleet.png"
                case .Wind:
                    imageName = "wind.png"
                case .Fog:
                    imageName = "fog.png"
                case .Cloudy:
                    imageName = "cloudy.png"
                case .PartlyCloudyDay:
                    imageName = "cloudy-day.png"
                case .PartlyCloudyNight:
                    imageName = "cloudy-night.png"
                }

            } else {
                imageName = "default.png"
            }



            return UIImage(named: imageName)

        }

    }
}

//end