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surround and surroundK added to Resource #1368

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merged 3 commits into from
Nov 6, 2020
Merged

surround and surroundK added to Resource #1368

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eaa456b
surround and surroundK added to Resource
pkowalcze Oct 29, 2020
0bd5660
Remove subtyping relationship between surroundee and resource
kubukoz Oct 30, 2020
dda1b39
improved scaladoc for surround and surroundK
pkowalcze Nov 6, 2020
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19 changes: 19 additions & 0 deletions core/shared/src/test/scala/cats/effect/ResourceSpec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -470,6 +470,25 @@ class ResourceSpec extends BaseSpec with ScalaCheck with Discipline {
// }
// }

"surround - should wrap an effect in a usage and ignore the value produced by resource" in ticked {
implicit ticker =>
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val r = Resource.liftF(IO.pure(0))
val surroundee = IO(1)
val surrounded = r.surround(surroundee)

surrounded eqv surroundee
}

"surroundK - should wrap an effect in a usage, ignore the value produced by resource and return FunctionK" in ticked {
implicit ticker =>
val r = Resource.liftF(IO.pure(0))
val surroundee = IO(1)
val surround = r.surroundK
val surrounded = surround(surroundee)

surrounded eqv surroundee
}

}

{
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14 changes: 14 additions & 0 deletions kernel/shared/src/main/scala/cats/effect/kernel/Resource.scala
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Expand Up @@ -417,6 +417,20 @@ sealed abstract class Resource[+F[_], +A] {
*/

private[effect] def invariant: Resource.InvariantResource[F0, A]

/**
* Wraps an effect in a usage and ignores the value produced by resource.
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I would change this scaladoc to something like:

acquires the resource, runs `gb`, and closes the resource once `gb` terminates, fails or gets interrupted

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Sounds good 👍 And for surroundK would the following be ok?

Creates a FunctionK that can run `gb` within a resource, which is then closed once `gb` terminates, fails or gets interrupted

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Updated the scaladoc

*/
def surround[G[x] >: F[x]: Resource.Bracket, B >: A](gb: G[B]): G[B] =
use(_ => gb)

/**
* Creates a FunctionK that wraps an effect in a usage when applied. Value produced by the resource is ignored.
*/
def surroundK[G[x] >: F[x]: Resource.Bracket]: G ~> G =
new (G ~> G) {
override def apply[B](gb: G[B]): G[B] = use(_ => gb)
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}
}

object Resource extends ResourceInstances with ResourcePlatform {
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