Unhelpful error message when associated type needs lifetime annotation

[seanmonstar]

Chopped code that shows this error:

fn with_connector<C: NetworkConnector>(connector: &mut C) -> HttpResult<Request> {
    let stream = try!(connector.connect(host, port, scheme));
    let stream = BufferedWriter::new(box stream as Box<NetworkStream + Send>);
    //                               ^~~ parameter `C` may not live long enough, consider an explicit lifetime 'static
}

pub trait NetworkConnector {
    type Stream: NetworkStream + Send;

    pub fn connect(...) -> IoResult<Self::Stream>;
}

Code fixed. Note that the lifetime wasn't need on C, though the error message says it was.

fn with_connector<'a, C: NetworkConnector<Stream = T>, T: NetworkStream+'a>(connector: &C) -> Result<Box<NetworkStream + 'a>, ()> {
    let stream = try!(connector.connect());
    Ok(box stream as Box<NetworkStream + 'a>)
}

trait NetworkStream {}

pub trait NetworkConnector {
    type Stream: NetworkStream;

    fn connect(&self) -> Result<Self::Stream, ()>;
}

/cc @nick29581

[nrc]

cc @nikomatsakis

[nikomatsakis]

Weird. Another option is to put C::Stream : 'a

[steveklabnik]

Triage: it's been a year, and without the full code, this is hard to reproduce. Any idea what the rest of it should be, @seanmonstar ?

[seanmonstar]

I do not really remember. I fixed it in my code and forgot this experience :)

[Mark-Simulacrum]

Without full code it's hard to figure out if this is still a bug; I'm going to close. If anyone can come up with an example that reproduces this please post and we'll reopen.