I want to do `String? -> Validated<E, String...

# arrow

[Emil Kantis]

I want to do String? -> Validated<E, String> -> Validated<E, A> (in my case converting a String? to UInt).

First step is easy with fromNullable, but I'm not sure how to map a validated while catching.. I think I'm looking for a mapCatching(handleError: (Throwable) -> E, f: (A) -> B) but it doesn't seem to exist? 🙂

[Emil Kantis]

inline fun <E, A, B> Validated<E, A>.mapCatching(handleError: (Throwable) -> E, f: (A) -> B): Validated<E, B> =
      fold(
         { it.invalid() },
         {
            try {
               f(it).valid()
            } catch (t: Throwable) {
               handleError(t).invalid()
            }
         },
      )

Is this bad practice?

[simon.vergauwen]

Such a method, or such extension methods are definitely not considered bad practice.

There is Validated.catch as well, and there is andThen.

inline fun <E, A, B> Validated<E, A>.mapCatching(handleError: (Throwable) -> E, f: (A) -> B): Validated<E, B> =
  andThen { a -> 
     Validated.catch { f(a) }
       .handleError(handleError)
  }

[Emil Kantis]

Ah, that's more elegant. Thank you 🙌