[ssokolow]

Java's ecosystem is moving away from checked exceptions because their "bolted onto the return type as a sidecar" design doesn't compose well with functional-style APIs.

Monadic error handling (Rust's Option<T>/Result<T, E>) avoids that issue by putting the error inside the return type as a normal value.

(Which is why, on multiple occasions, I've seen people call Result<T, E> "checked exceptions done right/properly".)

[kaba0]

> checked exceptions done right/properly

But they fail at including a stacktrace, autobubbling up, auto-unwrap and customizable "hit radius" with a try-catch block (okay, I'm sure some Monadic construct allows for that, but e.g. Rust's version does not).

[ssokolow]

1. Remember that Rust takes a Minimum Viable Product approach to 1.0 releases. There are experiments in adding stack traces in third-party error-handling crates that could eventually lead to additions to the standard library, but we've already gone through at least three iterations (error-chain, failure, anyhow, and possibly eyre) and already have two deprecated methods forever stuck on the standard library Error trait, so they're taking it slowly.

(Plus, true exception handling is messy for a language that cares so much about FFI. Look at the discussions surrounding how panic! unwinding should behave at FFI boundaries.)

2. I think completely automatic bubbling would be a misfeature, and the `?` operator is a good balance between concise ease-of-use and the Rust focus on "code is read far more often than it's written".

3. Again, the `?` operator. I think completely automatic unwrap would also be a massive footgun and comprehension hazard.

4. As mentioned in the other reply, try blocks are in development. (See my previous comment about Rust adopting a Minimum Viable Product approach to v1.0)

https://caniuse.rs/ is a great illustration of how far we've already come and how minimal Rust 1.0 was.

[steveklabnik]

Try blocks exist in Rust nightly, but given that an IIFE closure gives nearly the same results, there hasn't been a ton of pressure to stabilize them. I wish the team would though.