IO에서 오류 처리

값으로서의 오류

오류 발생시키기

import cats.effect.IO

val failed: IO[Int] =
  IO.raiseError(new RuntimeException("boom"))

handleError

import cats.effect.IO

val safe: IO[Int] =
  IO.raiseError[Int](new RuntimeException("x"))
    .handleError(_ => -1)

handleErrorWith

import cats.effect.IO

val recovered: IO[Int] =
  IO(throw new RuntimeException("fail"))
    .handleErrorWith(e => IO.println(s"caught: ${e.getMessage}").as(0))

attempt

import cats.effect.IO

val e: IO[Either[Throwable, Int]] =
  IO.raiseError[Int](new RuntimeException("oops")).attempt

attempt 패턴 매칭

import cats.effect.IO

val prog: IO[Unit] = IO(10 / 2).attempt.flatMap {
  case Right(v) => IO.println(s"ok: $v")
  case Left(e)  => IO.println(s"err: ${e.getMessage}")
}

redeem

import cats.effect.IO

val label: IO[String] =
  IO(42).redeem(e => s"failed: $e", v => s"value: $v")

redeemWith

import cats.effect.IO

val prog: IO[Unit] = IO(42).redeemWith(
  e => IO.println(s"err: $e"),
  v => IO.println(s"got: $v")
)

guarantee로 정리하기

import cats.effect.IO

val prog: IO[Int] =
  IO(compute()).guarantee(IO.println("done"))

def compute(): Int = 7

실패 시 재시도하기

import cats.effect.IO

def retry[A](io: IO[A], n: Int): IO[A] =
  if (n <= 0) io
  else io.handleErrorWith(_ => retry(io, n - 1))

일반 Scala의 try/catch

object Main {
  def main(args: Array[String]): Unit = {
    val result = try { 10 / 0 } catch { case _: ArithmeticException => -1 }
    println(s"result: $result")
  }
}

빠른 확인

요약