Comment by foresterre
5 hours ago
The Try trait (representing the ? the operation) is super cool though! I wish it was marked stable so you could implement it for types without using the nightly compiler.
Note that both Option and Result implement that same trait.
Perhaps if try blocks ever become a thing... we can finally use it for our own types ;)
The modern Try trait (try_v2) is indeed wonderful and I hope to see it stabilized one day.
AIUI a key innovation is ControlFlow, reifying the Break/ Continue choice as a sum type in the type system. This is already stable and is a useful piece of vocabulary even without its contribution to understanding the Try trait.
Knowing that Bob's CircusPerformance trait and Sarah's SeaLion type both use ControlFlow to decide whether we should keep going or halt ASAP means you don't have to write fraught adaptor code because Bob thought obviously the boolean "true" means keep going while Sarah's understanding was that it's a signal about being finished, so "true" means stop.
For Try what ControlFlow did was unlock the difference between "Success / Failure" as encoded by Result::Ok and Result::Err and the "Halt / Carry on" distinction ControlFlow::Break and ControlFlow::Continue. Often we want to stop when there's an error, but sometimes we mean the exact opposite, carry on trying things until one of them succeeds.