ensuring

[sidnt]

final def ensuring[R1 <: R](finalizer: URIO[R1, Any]): ZIO[R1, E, A]

• ensuring is a combinator available on all zio values
• since it is a combinator, it can combine two zio values,
  • the first with the second (the finalizer) to yield the third (the composite) description
• the second zio, is an effect, and
  • it is not allowed to fail
  • it can bring in its additional environmental dependencies

what's up with R and R1 ??

• R is of the first effect
• R1 is of the composite effect
• when running the composite effect, the environment the composite effect is provided, should cater to the requirements of both, the first effect AND the finalizer
• ie, the provided environment should be usable as both, the environment for the first effect AND that of the finalizer
• if we constrain R1 to be a subtype of R, then an r1: R1 can be used as R,
• thus R1 can cater to the requirements of first effect ,
• // but how do we reconcile with the type the finalizer comes with and what's inferred?

example

• let's say the first effect has dependency on Random and the finalizer has dependency on Console then the composite effect has to have a dependency on both Random AND Console

  val z1: URIO[Random, Int] = nextInt
  val z2: URIO[Console, Unit] = putStrLn("hi")
  val z3: URIO[Random & Console, Int] = z1.ensuring(z2)

  a value of type Random & Console can be used as both, Random or Console because it is a subtype of Random and it is a subtype of Console.