Converting BoxStream to BoxFuture

Question

Converting BoxStream to BoxFuture

I have a function that returns BoxStream<(), io::Error>

and wants to convert this stream to Future

(or BoxFuture

), but I am having some problems with the compiler:

extern crate futures;

use futures::stream::BoxStream;
use std::io;

pub fn foo() -> BoxStream<(), io::Error> {
    unimplemented!()
}

fn main() {
    let a = foo().into_future();
}

And the error message:

error[E0277]: the trait bound `futures::Stream<Error=std::io::Error, Item=()> + std::marker::Send + 'static: std::marker::Sized` is not satisfied
  --> src/main.rs:23:19
   |
23 |     let a = foo().into_future();
   |                   ^^^^^^^^^^^ the trait `std::marker::Sized` is not implemented for `futures::Stream<Error=std::io::Error, Item=()> + std::marker::Send + 'static`
   |
   = note: `futures::Stream<Error=std::io::Error, Item=()> + std::marker::Send + 'static` does not have a constant size known at compile-time

Is there a way to get around this?

+3

compiler-errors rust

Peter Jankuliak Apr 28 17 at 20:53

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1 answer

Shepmaster · Accepted Answer · 2017-04-28T22:11:16+0000

You are calling futures::future::IntoFuture::into_future

, not futures::stream::Stream::into_future

. You need to import the trait:

extern crate futures;

use futures::Stream; // This
use futures::stream::BoxStream;
use std::io;

pub fn foo() -> BoxStream<(), io::Error> {
    unimplemented!()
}

fn main() {
    let a = foo().into_future();
}

You can check the difference with

fn main() {
    let a = futures::future::IntoFuture::into_future(foo());
    let a = futures::Stream::into_future(foo());
}

Converting BoxStream to BoxFuture

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