Is there a built-in variant of Either/Validated `catch` that only handles specific exceptions and th...

# arrow

[Stewart Stewart]

Is there a built-in variant of Either/Validated catch that only handles specific exceptions and throws the rest?

[thanh]

I have a function for your usecase:

inline fun <R> catch(f: () -> R, predicate: (Throwable) -> Boolean): Either<Throwable, R> =
  try {
    f().right()
  } catch (t: Throwable) {
    t.nonFatalOrThrow()
    if (predicate(t.nonFatalOrThrow())) t.left()
    else throw t
  }

So we can use it like catch(f) {it as SpecificException}

[Giulio Caccin]

i’m a beginner and i found myself using

inline fun <A, B> Either<A, B>.filterLeft(predicate: (A) -> Boolean, default: () -> B): Either<A, B> =
    swap().filterOrElse(predicate, default).swap()

to handle it in the flow, but i would like to improve this so i think also your catch is great

[Stewart Stewart]

@thanh wouldn’t as result in a class cast exception?
I ended up playing with a version that used a type parameter, but it requires specifying R explicitly as well.