Can someone point me to a summary of how the inter...

# arrow

[David Hamilton]

Can someone point me to a summary of how the internal implementation for computation short-circuiting works for either ?
Also, has this internal approach changed for Arrow 1.2 (as well as the obvious change for Raise<E> )?

[Riccardo Cardin]

Hey, David. I explained it in this article: https://blog.rockthejvm.com/functional-error-handling-in-kotlin-part-3/

[Riccardo Cardin]

Hope it helps.

[Youssef Shoaib [MOD]]

Looking at the internal implementation definitely helps a lot too, but if you want the TL;DR: when you raise(), a RaiseCancellationException (usually the NoTrace version of it because it's more efficient) is thrown, and inside it contains your Raise instance, and the value you raised. Then, every fold block (which all raise builders ultimately call) will end up identity-checking that RaiseCancellationException.raise === expectedRaiseInstance. If that's true, then it casts the value to the expected type, and it's passed to the recover: (Error) -> R lambda that fold accepts.
It all boils down to myRaise.raise(errorVal) == throw RaiseCancellationException(myRaise, errorVal) and fold == try { block(myRaise) } catch(e: CancellationException) { recover(e.raisedOrRethrow(myRaise)) } where e.raisedOrRethrow(myRaise) == if(e is RCE && e.raise == myRaise) e.value else throw e

[Youssef Shoaib [MOD]]

It used to be much more complicated with coroutines magic, but this is definitely the safest and most efficient way of doing it without something like a compiler plugin. It's practically as safe as coroutine cancellation is, because coroutine cancellation uses a CancellationException, which RCE inherits from

[David Hamilton]

@Youssef Shoaib [MOD] Thank you - I suspected that was the case, but my understanding of the internals was not strong enough for me to be sure. Very helpful thank you color

[David Hamilton]

@Riccardo Cardin Your articles are some of the most amazing technical deep-dives I've read. Unfortunately I'd only got part way through that one, and hadn't realised that it contained the answer I needed! Look forward to reading the rest!

[Riccardo Cardin]

No problem. I should have pointed you to the right point from the beginning 😅