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Box<T> used to be ~T early on in rust… (then it became a `box` keyword, before being removed entirely.) They got rid of it because they wanted to move more things into libraries and have a less opinionated compiler.

I think I agree though, especially with Option. Swift’s option syntax (and kotlin’s which is similar) is so much better, a simple question mark in the type. Options are important enough that dedicated syntax makes so much sense. Rust blew their chance here with ? meaning “maybe early return”, it would have been a lot more useful as an Option indicator.

by kibwen2 hours ago|

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I used to think this too, but nowadays I think this would have been a mistake. Result is actually the more important and fundamental type, not Option, and giving Option special syntax would cause people to want to favor it over Result even when it shouldn't be. If anything, I think that `?` should have been reserved as a suffix for function names (not types) that return Result, so that instead of `fn try_foo()` and `let x = try_foo();` we could have `fn foo?()` and `let x = foo?();`, and then the current `?` operator could just be spelled `.try`, akin to `.await`. (And then we maybe could go further and reserve `!` as a suffix for functions that can panic...)

by foresterre2 hours ago|

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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 ;)

https://doc.rust-lang.org/std/ops/trait.Try.html

by tialaramex43 minutes ago|

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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.