Cannot declare a satisfiable feed reference

[telamon]

Question

Your Environment

Software	Version(s)
hypercore	0.9.0
Rustc	rustc 1.34.1 (fc50f328b 2019-04-24)
Operating System	linux

Question

So I'm not sure if I should ask this question here. I have tried to find help elsewhere but writing here as a last-resort. I'm new to rust and I have been picking up the language at a steady pace. But there's one issue that I've been struggling with to the point of insanity.

How do you store a hypercore::Feed in a struct or define a function that can take a feed as a parameter?

// What is the correct type declaration for feed? 
pub struct MyStruct {
  m_feed: Feed<RandomAccess>,
}; 

pub fn (a_feed: &Feed<RandomAccess>) { ... }

// Or even slightly modifying the example from the docs:
let path = PathBuf::from("./my-first-dataset");
let mut feed: TYPE_DECLARATION = Feed::new(&path).unwrap();

I've literally spent a week trying all kinds of exotic declaration to satisfy the compiler traits, but to no avail..

Again humble apologies for asking this here, please help!

[yoshuawuyts]

@telamon no worries, it's always okay to ask (:

Getting a better idea of what you're looking at would be helpful. I'm not sure what you're running into. Screenshots would be good, text output would be better, a git repo that can be cloned and run to reproduce your error would be best.

Thanks!

[telamon]

@yoshuawuyts Thank you for the reply. Sorry if my question was a bit unclear, essentially I'd like to know how to define a struct capable of holding a Feed or a method that could take a reference to a Feed. Due to the design of the RandomAccess trait I cannot figure out how to declare my struct letalone define a variable that will be able to hold it without using the automatic type declaration.

Here is an example I ended up with following compiler errors:

use hypercore::Feed;
use random_access::RandomAccess;
use std::path::PathBuf;

#[test]
fn it_works() {
    let storage_path = PathBuf::from("/tmp/a");
    let mut feed: Feed<RandomAccess<Error = failure::Error>> = hypercore::Feed::new(&storage_path).unwrap();
    //            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   // I simply can't figure out the correct type format to satisfy the compiler.
}

The above snippet produces the following error:

   Compiling ciphercore v0.1.0 (/home/telamon/lpro/hyper-rs/ciphercore)
error[E0277]: the size for values of type `dyn random_access_storage::RandomAccess<Error=failure::error::Error>` cannot be known at compilation time
  --> tests/test.rs:10:19
   |
10 |     let mut feed: Feed<RandomAccess<Error = failure::Error>> = hypercore::Feed::new(&storage_path).unwrap();
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `std::marker::Sized` is not implemented for `dyn random_access_storage::RandomAccess<Error=failure::error::Error>`
   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
   = note: required by `hypercore::Feed`

Omitting Error = failure::Error as argument to RandomAccess<> makes the compiler complain about a missing argument, just like omitting RandomAccess from from Feed<> produces the same compiler complaint.

Ultimately I would just like to define a struct with a feed...

pub struct MyStruct {
 a_feed: ??Type??
}