Oh yeah, I can totally relate to the Send-Sync-Unpin massaging, plus 'static bound for me. It's so weird that individually each of them kinda makes sense, but often you need to combine then and all of a sudden the understanding of combinations just does not.. combine. After a minute or two of trying to figure out what should actually go into that bound I give up, remove all of them and start adding them back one by one until the compiler is happy.
Yep. Same. I've been doing Rust for years at this point (not full time, and with long gaps- granted), and it's exactly like you said: individually these things are simple, but then you're trying to figure out where you accidentally let a reference cross an await boundary that killed your automatic Unpin that you didn't realize you needed. Suddenly it feels like you don't understand it like you thought you did.
The static lifetime bound is annoying, too! I guess it crops up if you take a future and compose it with another one? Both future implementations have to be static types to guarantee they live long enough once passed into the new future.
