Swift 对异步编程有哪些语言级别的支持（如果有）

Swift 是一种现代化的编程语言，它提供了强大的异步编程支持。在 Swift 中，我们可以使用多种方式来处理异步任务，包括异步函数、异步闭包、异步序列和异步/等待。下面将详细介绍 Swift 对异步编程的语言级别支持。

swift
func getUserInfo(completion: @escaping (String, Int) -> Void) async {
    // 模拟异步获取用户信息
    await Task.sleep(2 * NSEC_PER_SEC)
    
    let name = "John"
    let age = 25
    
    completion(name, age)
}
async {
    let userInfo = await getUserInfo()
    print("Name: \(userInfo.0), Age: \(userInfo.1)")
}

swift
func downloadFile(completion: @escaping (Data?, Error?) -> Void) {
    // 模拟异步下载文件
    DispatchQueue.global().async {
        // 模拟下载耗时
        Thread.sleep(forTimeInterval: 3)
        
        let fileData = Data()
        completion(fileData, nil)
    }
}
async {
    let fileData = await withUnsafeContinuation { continuation in
        downloadFile { (data, error) in
            if let data = data {
                continuation.resume(returning: data)
            } else {
                continuation.resume(throwing: error ?? NSError())
            }
        }
    }
    
    // 下载完成后的处理
    print("Downloaded file with size: \(fileData.count)")
}

swift
struct FibonacciSequence: AsyncSequence {
    typealias Element = Int
    
    struct AsyncIterator: AsyncIteratorProtocol {
        var current = (0, 1)
        let count: Int
        
        mutating func next() async -> Int? {
            guard count > 0 else {
                return nil
            }
            
            count -= 1
            
            let nextValue = current.0
            current = (current.1, current.0 + current.1)
            
            return nextValue
        }
    }
    
    let count: Int
    
    func makeAsyncIterator() -> AsyncIterator {
        return AsyncIterator(count: count)
    }
}
async {
    for await number in FibonacciSequence(count: 10) {
        print(number)
    }
}

swift
func fetchData() async throws -> Data {
    // 模拟异步获取数据
    await Task.sleep(2 * NSEC_PER_SEC)
    
    // 模拟抛出错误
    throw NSError(domain: "com.example", code: -1, userInfo: nil)
}
async {
    do {
        let data = try await fetchData()
        print("Fetched data with size: \(data.count)")
    } catch {
        print("Failed to fetch data: \(error)")
    }
}