Resultify

Resultify.swift

enum ResultError: Error { case emptyData }

func resultify<T>(_ completion: @escaping (Result<T, Error>) -> Void) -> (T?, Error?) -> Void {
    return { data, error in
        if let error = error {
            completion(.failure(error))
        } else if let data = data {
            completion(.success(data))
        } else {
            completion(.failure(ResultError.emptyData))
        }
    }
}

func resultify<T, U>(_ completion: @escaping (Result<(T?, U?), Error>) -> Void) -> (T?, U?, Error?) -> Void {
    return { data1, data2, error in
        if let error = error {
            completion(.failure(error))
        } else {
          // with 2 parameters, we can't verify if there is no data :
          // What to do when data1 is nil and not data2, and vice versa ?
            completion(.success((data1, data2)))
        }
    }
}

// Use :

// 1. URLSession
let urlSession = URLSession(configuration: .default)
let url = URL(string: "https://google.com")!
urlSession.dataTask(with: url, completionHandler: resultify { result in
    switch result {
    case .failure(let error):
        print("error : \(error)")
    case .success(let success):
        let data = success.0 // Data?
        let response = success.1 // URLResponse?

    }

})

// 2. CloudKit
let record = CKRecord(recordType: "Foo")
record["date"] = Date()

database.save(record, completionHandler: resultify { result in
	switch result {
    case .failure(let error):
        print("error : \(error)")
    case .success(let successedRecord): // CKRecord
		print("saved : \(successedRecord)")
    }
})