In general, Rust's big binaries are one of the things that puts me off the most. Even dynamic linking often doesn't help much. Then again, if a few MB, which is a rounding error nowadays, is among the worst I can think of, that's actually pretty amazing ;).

Rust's Futures allow for easy chaining, whereas I only implemented a simple callback that runs on completion, but it doesn't allow one to get at the computed value directly. I simply send a "check for updates" event there. Instead the value gets stored in a Mutex and has to be pulled out of that explicitly, although it can stay in the "Async" type, just that it gets stored directly in the struct after it's pulled out of the Mutex. The advantage is you don't have to pay for the locking all the time and the value can stay where it is, so you don't need to juggle it around. You can see it here: https://github.com/rabite0/hunter/blob/master/src/preview.rs...

I started working on an improved version that actually allows for a callback with a reference to the value upon completion and also a callback that moves the value out, but I haven't finished that yet and after seeing this I might not ever, but I probably will, since it's definitely educative.