Alamofire 和 URLSession 的一个对比例子

[Livid]

https://medium.com/swift-programming/alamofire-vs-urlsession-a-comparison-for-networking-in-swift-c6cb3bc9f3b8

同样的一个需求，用 AF 实现：

AF.request("https://api.mywebserver.com/v1/board", method: .get, parameters: ["title": "New York Highlights"])
    .validate(statusCode: 200..<300)
    .responseDecodable { (response: DataResponse) in
        switch response.result {
        case .success(let board):
            print("Created board title is \(board.title)") // New York Highlights
        case .failure(let error):
            print("Board creation failed with error: \(error.localizedDescription)")
        }
}

用 URLSession 实现：

enum Error: Swift.Error {
    case requestFailed
}

// Build up the URL
var components = URLComponents(string: "https://api.mywebserver.com/v1/board")!
components.queryItems = ["title": "New York Highlights"].map { (key, value) in
    URLQueryItem(name: key, value: value)
}

// Generate and execute the request
let request = try! URLRequest(url: components.url!, method: .get)
URLSession.shared.dataTask(with: request) { (data, response, error) in
    do {
        guard let data = data,
            let response = response as? HTTPURLResponse, (200 ..< 300) ~= response.statusCode,
            error == nil else {
            // Data was nil, validation failed or an error occurred.
            throw error ?? Error.requestFailed
        }
        let board = try JSONDecoder().decode(Board.self, from: data)
        print("Created board title is \(board.title)") // New York Highlights
    } catch {
        print("Board creation failed with error: \(error.localizedDescription)")
    }
}

[pupboss]

其实 AF 只是替开发者执行了 let board = try JSONDecoder().decode(Board.self, from: data)

然后 AF 使用了 Swift 语言特性 Result 类型，上面这个 AF 的例子过于简化了，实际项目也不会这么短的

https://developer.apple.com/documentation/swift/result

[ming1016]

可以搭配着 Combine 来用，assign 给 ViewModel 的数据属性和 SwiftUI 绑定在一起，响应式交互。
```swift
URLSession.shared.dataTaskPublisher(for: req)
.map { data, res in
print(String(decoding: data, as: UTF8.self))
return data
}
.mapError { _ in
APISevError.resError
}
.decode(type: Request.Res.self, decoder: de)
.mapError(APISevError.parseError)
.receive(on: RunLoop.main)
.eraseToAnyPublisher()
```
绑定部分代码
```swift
repStream = resSubject
.map {
$0.items
}
.assign(to: \.repos, on: self)
```