asyncSequence.swift

enum RequestError: Error {
    case apiError(reason: String)
}

class AsyncJokeGenerator: AsyncSequence {
    __consuming func makeAsyncIterator() -> AsyncIterator {
        return AsyncIterator(numberOfJokes: numberOfJokes)
    }
    typealias Element = String

    private let numberOfJokes: Int
    init(numberOfJokes: Int) {
        self.numberOfJokes = numberOfJokes
    }

    struct AsyncIterator: AsyncIteratorProtocol {
        var numberOfJokes: Int = 0
        mutating func next() async throws -> String? {
            if numberOfJokes > 0 {
                numberOfJokes -= 1
                return try await giveMeAJoke()
            } else {
                return nil
            }
        }

        private func giveMeAJoke() async throws -> String {
            return try await getJSONResult(url: "https://api.chucknorris.io/jokes/random", key: "value")
        }

        private func getJSONResult(url: String, key: String) async throws -> String {
            let (data, _) = try await URLSession.shared.data(from: URL(string: url)!, delegate: nil)

            if let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String: Any],
                let result = json[key] as? String {
                return result
            } else if let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [[String: Any]],
                      let result = json.first?[key] as? String {
                return result
            } else {
                throw RequestError.apiError(reason: "JSON parse error")
            }
        }
    }
}

async {
    for try await joke in AsyncJokeGenerator(numberOfJokes: 3) {
        print(joke)
    }
}