带有 async/await 的 Swift Playground“无法在范围内找到‘async’”

Question

我正在尝试在 Xcode Playground 上运行这个异步函数：

import Foundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

enum NetworkingError: Error {
    case invalidServerResponse
    case invalidCharacterSet
}

func getJson() async throws -> String {
        let url = URL(string:"https://jsonplaceholder.typicode.com/todos/1")!
        let (data, response) = try await URLSession.shared.data(from: url)
        
        guard let httpResponse = response as? HTTPURLResponse,
              httpResponse.statusCode == 200 else {
                  throw NetworkingError.invalidServerResponse
              }
        
        guard let result = String(data: data, encoding: .utf8) else {
            throw NetworkingError.invalidCharacterSet
        }
        
        return result
}
    
let result = try! await getJson()
print(result)

我收到此错误消息：

error: ForecastPlayground.playground:27:25: error: 'async' call in a function that does not support concurrency
let result = try! await getJson()
                        ^

所以我尝试在我的 func 调用中创建 async 块：

async{
    let result = try! await getJson()
    print(result)
}

然后我收到了这个错误消息：

Playground execution failed:

error: ForecastPlayground.playground:27:1: error: cannot find 'async' in scope
async{
^~~~~

我尝试使用新的 @MainActor 属性注释我的函数，但它不起作用。

我做错了什么？

Answer 1

添加导入_Concurrency（下划线，因为默认情况下应该包含它）或使用该库的库，例如UIKit或SwiftUI。不过，Swift Playgrounds 目前似乎无法访问所有并发功能，例如async let.

总之

import _Concurrency