I am looking for a way to combine several validation errors using the raise DSL when there is no res...

# arrow

[Ulrich Schuster]

I am looking for a way to combine several validation errors using the raise DSL when there is no result to return. While there is forEachAccumulating instead of mapOrAccumulate when I am only interested in the errors, there does not seem to be a similarly complementarey function to zipOrAccumulate, is there?
What I suppose I need is something along those lines:

fun RaiseAccumulate<MyError>.ensureIsValid(myIdString: String) =
        ensureAccumulate( // this function does not exist
            { ensure( someCondition1(myIdString) ) { IncorrectCondition1(myIdString) } },
            { ensure( Dsomecondition2(myIdString) ) { IncorrectCondition2(myIdString) } }
        )

[Alejandro Serrano.Mena]

at this moment, unfortunately you need to write something along the lines of

zipOrAccumulate(
  { ensure(...) }
  { ensure(...) }
) { }

however, in the 2.0 to be released soon, you've be able to write much nicer code

accumulate {
  ensureAccumulating(thing1) { ... }
  ensureAccumulating(thing2) { ... }
}

[Riccardo Cardin]

Wow! That's great! I'm curious: what’s the returning type of the ensureAccumulating function? I mean, in case of an error, you need to return something to let the execution proceed

[Alejandro Serrano.Mena]

just Unit

[Riccardo Cardin]

Ok. The semantic is different from zipOrAccumulate then. You can’t return a valid object as the return of the accumulate function. Did I get it wrong?

[Alejandro Serrano.Mena]

no, you definitely can. The DSL in that case encourages using delegated properties

accumulate {
  val name by validateName(rawName).bindOrAccumulate()
  val age by validateAge(rawAge).bindOrAccumulate()
  Person(name, age)
}

[Riccardo Cardin]

Thanks, Alejandro 🙏. I need to check the implementation to understand it better. By the way, it’s a nice DSL improvement 🙌

[Alejandro Serrano.Mena]

the main "trick" is that by using delegated properties we can delay the "bind" aspect to the moment in which the first variable is read. The code above actually compiles under the hood to:

accumulate {
  val name: Value<Name> = validateName(rawName).bindOrAccumulate()
  val age: Value<Age> = validateAge(rawAge).bindOrAccumulate()
  Person(name.getValue(), age.getValue())
}

during the bindOrAccumulate (or any other accumulation function) we simply accumulate any errors in a temporary list. In the first call to getValue() we check that list, and it's there's something, we just raise the corresponding set of errors.

unfortunately this is something which drinks a lot from Kotlin's delegated properties feature; I'm sure you can transpose it to Swift, but I'm not so sure about other languages...

[Riccardo Cardin]

but I’m not so sure about other languages...

In fact, I was thinking about how to transpose it into Scala 😅
By the way, big shout-out 👏