Rejecting Some Success Values

We can reject some success values using the ZIO#reject operator:

trait ZIO[-R, +E, +A] {
  def reject[E1 >: E](pf: PartialFunction[A, E1]): ZIO[R, E1, A]

  def rejectZIO[R1 <: R, E1 >: E](
    pf: PartialFunction[A, ZIO[R1, E1, E1]]
  ): ZIO[R1, E1, A]
}

If the PartialFunction matches, it will reject that success value and convert that to a failure, otherwise it will continue with the original success value:

import zio._

val myApp: ZIO[Any, String, Int] =
  Random
    .nextIntBounded(20)
    .reject {
      case n if n % 2 == 0 => s"even number rejected: $n"
      case 5               => "number 5 was rejected"
    }
    .debug