Question

我有一个异步特征方法，该方法返回std Future：

Pin<Box<dyn Future<Output = Result<Vec<ResultType>, Box<(dyn Error + 'static)>>> + Send>>

ResultType是性状的关联类型，Sync + Send。

请注意，此类型不能取消固定。

我想从actix处理程序中调用它，然后对结果进行一些处理。

例如：

impl StreamHandler<ws::Message, ws::ProtocolError> for MyActor {
    fn handle(&mut self, msg: ws::Message) {
        let fut = get_future();
        let actor_fut = fut
            .into_actor(&self)
            .map(|r, _actor, ctx| {
                ctx.text(r.map(|| ...))
            });

        ctx.spawn(actor_fut);
    }
}

此操作失败，因为into_actor拥有对未来的所有权，而Pin不允许这样做。清除的错误消息如下：

error[E0599]: no method named `into_actor` found for type `Pin<Box<dyn Future<Output = Result<Vec<ResultType>, Box<dyn Error>>> + Send>>` in the current scope
   --> src/app_socket.rs:194:26
    |
194 |                         .into_actor(&self)
    |                          ^^^^^^^^^^ method not found in `Pin<Box<dyn Future<Output = Result<Vec<ResultType>, Box<dyn Error>>> + Send>>`
    |
    = note: the method `into_actor` exists but the following trait bounds were not satisfied:
            `&dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send : WrapFuture<_>`
            `&dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send : WrapStream<_>`
            `&mut dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send : WrapFuture<_>`
            `&mut dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send : WrapStream<_>`
            `&mut Pin<std::boxed::Box<dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send>> : WrapFuture<_>`
            `&mut Pin<std::boxed::Box<dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send>> : WrapStream<_>`
            `&Pin<std::boxed::Box<dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send>> : WrapFuture<_>`
            `&Pin<std::boxed::Box<dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send>> : WrapStream<_>`
            `dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send : WrapFuture<_>`
            `dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send : WrapStream<_>`
            `Pin<std::boxed::Box<dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send>> : WrapFuture<_>`
            `Pin<std::boxed::Box<dyn Future<Output = Result<std::vec::Vec<ResultType>, std::boxed::Box<dyn std::error::Error>>> + Send>> : WrapStream<_>`

我该怎么做？

Answer 1

实际的问题不是锁定未来，而是实现了错误的未来特征。

This section on Pinning解释说poll是为Pin<ref T: Future>实现的。

因此，into_actor签名self: impl Future -> WrapFuture<_>很好。问题在于，async方法返回了将来实现的std::future::Future，而into_actor则期望futures01::future::Future。

将来在致电.compat()之前致电.into_actor可以解决此问题。

有关转换期货的更多详细信息，请参见this post。

如何从actix处理程序中调用固定未来？

1 个答案: