Swift4の機能を活用してGoogle画像検索結果を利用する

Google画像検索APIをiOSで利用する - Qiita
https://qiita.com/ukandori/items/234156f97eb6dad77966
などの先人を参考に。Codableや新しいreduceURLComponentsを使ったらだいぶシンプルになりました。
(追記)コメントを受けて、URLComponentsに書き替えました。こちらのほうがStringでやるより適切ですね。

// Structure defined by https://developers.google.com/custom-search/json-api/v1/reference/cse/list#response
struct CustomSearchedResult: Codable {
    struct Item: Codable {
        struct Image: Codable {
            let contextLink: String
            let thumbnailLink: String
            let thumbnailHeight: Int
            let thumbnailWidth: Int
        }
        let link: URL
        let displayLink: URL
        let mime: String
        let image: Image
    }
    let items: [Item]
}

let query = "ほげほげ"
var urlComponents = URLComponents(string: "https://www.googleapis.com/customsearch/v1")!
urlComponents.queryItems = [
    URLQueryItem(name: "searchType", value: "image"),
    URLQueryItem(name: "q", value: query),
    // To get `key`, create your own project from https://console.developers.google.com/projectcreate
    URLQueryItem(name: "key", value: "xxxxxxx-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"),　
    // To get `cx`, create your own search engine from https://cse.google.com/cse/create/new
    URLQueryItem(name: "cx", value: "000000000000000000000:xxxxxxxxxxx")
]
print(urlComponents.string!)

let task = URLSession.shared.dataTask(with: urlComponents.url!) { data, response, error in
    guard let jsonData = data else {
        print(error as Any)
        return
    }

    do {
        let result = try JSONDecoder().decode(CustomSearchedResult.self, from: jsonData)
        print(result.items[0])

        let task = URLSession.shared.dataTask(with: result.items[0].link) {data, response, error in
            guard let image = data.flatMap(UIImage.init) else {
                print(error as Any)
                return
            }
            // imageとれた
        }
        task.resume()
    } catch(let e) {
        print(e)
    }
}
task.resume()