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attemptTap #3459

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merged 5 commits into from
Jul 5, 2020
Merged

attemptTap #3459

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cc9bf65
attemptTap
Jun 7, 2020
db58073
add to typeclass
Jun 16, 2020
00651a7
Merge branch 'master' into attempt-tap
Jun 16, 2020
6b462db
Add attemptTap example
Jun 16, 2020
f78dc92
Fix doc
Jun 17, 2020
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3 changes: 3 additions & 0 deletions core/src/main/scala/cats/syntax/monadError.scala
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Expand Up @@ -32,6 +32,9 @@ final class MonadErrorOps[F[_], E, A](private val fa: F[A]) extends AnyVal {

def redeemWith[B](recover: E => F[B], bind: A => F[B])(implicit F: MonadError[F, E]): F[B] =
F.redeemWith[A, B](fa)(recover, bind)

def attemptTap[B](f: Either[E, A] => F[B])(implicit F: MonadError[F, E]): F[A] =
F.rethrow(F.flatTap(F.attempt(fa))(f))
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I'm not sure exactly what common pattern this is replacing? I guess exactly what the implementation is doing?

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@RaasAhsan RaasAhsan Jun 9, 2020 •
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We already have an analogue for Future#onSuccess/Future#foreach (FlatMap#flatTap) and Future#onError (ApplicativeError#onError). This would be the pure analogue to Future#onComplete, which is useful for use cases like reporting metrics or logging. This function makes call chains a bit more compact.

fa
  .attempt
  .flatTap {
    case Right(a) => log.info(s"succeeded with $a")
    case Left(e) => log.error(s"failed with $e")
  }
  .rethrow

// Ironically this one has fewer LOC but harder to factor out the bodies
fa
  .flatTap(a => log.info(s"succeeded with $a"))
  .onError(e => log.error(s"failed with $e"))

fa.attemptTap {
  case Right(a) => log.info(s"succeeded with $a")
  case Left(e) => log.error(s"failed with $e")
}

aside: I could see an argument for accepting f as a PartialFunction

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Ah I see what you mean. Alrighty, I'm broadly 👍 on this then. Re your aside, I think the total function is better since Scala's PartialFunction/Function1 inheritance is backwards, so this is the more flexible arrangement.

}

final class MonadErrorRethrowOps[F[_], E, A](private val fea: F[Either[E, A]]) extends AnyVal {
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