Core::spawn should expect Error=Void not Error=()

[Rufflewind]

Since spawn never looks at the results of the future, the return value ought to be completely devoid of any useful information to reduce the risk that the user might unintentionally forget about the result.

The current choice of Future<Item=(), Error=()> still has one bit of information: it’s possible to distinguish between Ok(()) and Err(()) results. It really ought to return Future<Item=(), Error=Void>, which means the Future is guaranteed to succeed.

It’s not a big problem by any means, just kind of quirky in my perspective.

[alexcrichton]

Yes unfortunately there's no shared "void" type right now across these libraries. The futures crate for example has a number of situations where the error should be void vs () as it is today.

This is something that we'll definitely want to evaluate for futures 0.2

[vks]

What about using the void crate?

[carllerche]

I don't think we want to pull in another crate. Either way, changing the type will be a breaking change which requires a version bump.

I think at this point, we'll be better off waiting for upcoming changes to rust-lang to hit stable.

[srijs]

Just for reference, this is being discussed in futures as well: rust-lang/futures-rs#476

If futures ended up exporting Void I suppose tokio could leverage that?

[alexcrichton]

Indeed!