一个 AsyncTaskMethodBuilder 状态机示例

using System;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;

async Task Main()
{
    Task<int> task = CreateTask();
    int result = await task;
}

Task<int> CreateTask()
{
    // 创建一个异步任务方法构建器
    AsyncTaskMethodBuilder<int> builder = AsyncTaskMethodBuilder<int>.Create();

    // 获取构建器的状态机
    var stateMachine = new AsyncStateMachine(builder);

    // 将构建器设置为等待状态
    stateMachine.MoveNext();
    // 返回异步任务
    return builder.Task;
}

// 定义异步状态机
struct AsyncStateMachine : IAsyncStateMachine
{
    private AsyncTaskMethodBuilder<int> _builder;
    private int _result;

    public AsyncStateMachine(AsyncTaskMethodBuilder<int> builder)
    {
        _builder = builder;
        _result = 0;
    }

    public void MoveNext()
    {
        try
        {
            // 执行异步操作，这里以延迟 2 秒为例
            Task.Delay(2000).Wait();

            // 设置异步任务的结果
            _result = 42;
            // 设置值，任务结束
            _builder.SetResult(_result);
        }
        catch (Exception ex)
        {
            // 异常处理
            _builder.SetException(ex);
        }
    }

    public void SetStateMachine(IAsyncStateMachine stateMachine)
    {
        // 用不到，不处理
    }
}