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by majewsky 3006 days ago

I can see where the author comes from. I've been working with ^W^W fighting against Tokio this week, and the error messages are horrible. Representative example:

  error[E0271]: type mismatch resolving `<futures::AndThen<futures::Select<futures::stream::ForEach<futures::stream::MapErr<std::boxed::Box<futures::Stream<Error=std::io::Error, Item=(tokio_uds::UnixStream, std::os::ext::net::SocketAddr)> + std::marker::Send>, [closure@src/server/mod.rs:59:18: 59:74]>, [closure@src/server/mod.rs:60:19: 69:10 next_connection_id:_], std::result::Result<(), ()>>, futures::MapErr<futures::Receiver<()>, [closure@src/server/mod.rs:74:18: 74:74]>>, std::result::Result<(), ((), futures::SelectNext<futures::stream::ForEach<futures::stream::MapErr<std::boxed::Box<futures::Stream<Error=std::io::Error, Item=(tokio_uds::UnixStream, std::os::ext::net::SocketAddr)> + std::marker::Send>, [closure@src/server/mod.rs:59:18: 59:74]>, [closure@src/server/mod.rs:60:19: 69:10 next_connection_id:_], std::result::Result<(), ()>>, futures::MapErr<futures::Receiver<()>, [closure@src/server/mod.rs:74:18: 74:74]>>)>, [closure@src/server/mod.rs:78:34: 83:6 cfg:_]> as futures::Future>::Error == ()`
    --> src/server/mod.rs:85:15
     |
  85 |     return Ok(Box::new(server));
     |               ^^^^^^^^^^^^^^^^ expected tuple, found ()
     |
     = note: expected type `((), futures::SelectNext<futures::stream::ForEach<futures::stream::MapErr<std::boxed::Box<futures::Stream<Error=std::io::Error, Item=(tokio_uds::UnixStream, std::os::ext::net::SocketAddr)> + std::marker::Send>, [closure@src/server/mod.rs:59:18: 59:74]>, [closure@src/server/mod.rs:60:19: 69:10 next_connection_id:_], std::result::Result<(), ()>>, futures::MapErr<futures::Receiver<()>, [closure@src/server/mod.rs:74:18: 74:74]>>)`
                found type `()`
     = note: required for the cast to the object type `futures::Future<Item=(), Error=()>`

I have hope that things will improve on this front when `impl Trait` lands.

EDIT: After re-reading this, I want to add that I don't mean to hate on Tokio. I like the basic design very much, and hope that they can work out the ergonomics issues and stabilize the API soon.

7 comments

pimeys 3006 days ago

That's nothing!

      |
  212 | /     fn call(&self, payload: Self::Request) -> Self::Future {
  213 | |         let request = self.create_request(payload);
  214 | |
  215 | |         let work = async_block! {
  ...   |
  254 | |         FutureResponse(Box::new(work))
  255 | |     }
      | |_____^
  note: ...so that the type `impl futures::__rt::MyFuture<<[generator@src/client.rs:215:20: 252:10 self:&client::Client,

request:hyper::Request for<'r> {futures::Async<futures::__rt::Mu>, (), fn(std::result::Result<hyper::Response, error::Error>) -> std::result::Result<<std::result::Result<hyper::Response, error::Error> as std::ops::Try>::Ok, <std::result::Result<hyper::Response, error::Error> as std::ops::Try>::Error> {<std::result::Result<hyper::Response, error::Error> as std::ops::Try>::into_result}, futures::MapErr<hyper::client::FutureResponse, [closure@src/client.rs:217:59: 217:85]>, hyper::Response, std::option::Option<std::string::String>, &'r hyper::Response, hyper::StatusCode, fn(std::result::Result<hyper::Chunk, error::Error>) -> std::result::Result<<std::result::Result<hyper::Chunk, error::Error> as std::ops::Try>::Ok, <std::result::Result<hyper::Chunk, error::Error> as std::ops::Try>::Error> {<std::result::Result<hyper::Chunk, error::Error> as std::ops::Try>::into_result}, futures::stream::Concat2<futures::stream::MapErr<hyper::Body, [closure@src/client.rs:234:49: 234:75]>>}] as std::ops::Generator>::Return>` will meet its required lifetime bounds