제니스 사무소에서 Optional 출연.

let hoge: Any? = nil
hoge as! String?  // nil

func convert<T>(_ value: Any?) -> T {
    return value as! T
}

convert(nil) as String?  // fatal error: unexpectedly found nil while unwrapping an Optional value

func convert<T>(_ value: Any?) -> T {
    func cast<U, V>(_ value: U, to type: V.Type) -> V {
        return value as! V
    }
    return cast(value, to: T.self)
}

convert(nil) as String?  // nil

struct Hoge {
    let val1: String
    let val2: String?
}

Hoge(val1: convert(dict["val1"]),
     val2: convert(dict["val2"]))


// 逐一 `as` を書きたくない
Hoge(val1: dict["val1"] as! String,
     val2: dict["val2"] as? String)