这是快速将struct转换为future的方法，其中future实现是一个底层的 async fn。

请参阅此示例以获取详细信息 ...

  use ::auto_future::AutoFuture;

  struct ExampleStruct;

  impl ExampleStruct {
    async fn do_async_work(self) -> u32 {
      // perform a bunch of awaited calls ...

      123
    }
  }

  impl IntoFuture for ExampleStruct {
      type Output = u32;
      type IntoFuture = AutoFuture<u32>;

      fn into_future(self) -> Self::IntoFuture {
          let raw_future = self.do_async_work();
          AutoFuture::new(raw_future)
      }
  }