How can I store the result of a future where map_err has been chained?

help
#1

I have a future that I’m trying to store in a custom combinator. It’s always the same type: tokio::timer::Delay with an error mapped to () (for simplicity’s sake, though I may want to change this later).

let expire = Delay::new(expiry_time)
                  .map_err(|_| ());

I don’t know how to store this. Its type is MapErr<Delay, [closure]>, and when I try to box the closure, it won’t work with the map_err function.

#2

The easiest way is to put it on the heap, giving it the type Box<Future<Item=(), Error=()>>. See: https://play.rust-lang.org/?version=stable&mode=debug&edition=2015&gist=25a4f78315cd03cbf1454715dc7be2d6

#3

Oh sorry, should have read more closely that you already tried boxing, but you just tried boxing the closure. Try boxing the whole future, unless there’s a reason not to do that.

#4

Can also store it in MapErr<Delay, fn(Error)> if you need to name the type.

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#5

Box<Future<Item=(), Error=()>> ended up working out well! I think I had tried boxing the whole future, but I hadn’t specified some of the types correctly.

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