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Add a map method directly onto Resource #437

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merged 6 commits into from
Dec 6, 2018
Merged

Add a map method directly onto Resource #437

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619087d
Add a `map` method directly onto `Resource`
andimiller Dec 3, 2018
cb35949
Implement Resource.map using pure rather than makeCase
andimiller Dec 3, 2018
2831aa8
Weaken F on Resource.map to Applicative, since pure only needs Applic…
andimiller Dec 3, 2018
6cbfc56
whitespace
andimiller Dec 3, 2018
bff26b1
Use Resource.map within Resource Monad
andimiller Dec 3, 2018
d0877cd
Give Resource.map more useful scaladoc
andimiller Dec 3, 2018
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10 changes: 10 additions & 0 deletions core/shared/src/main/scala/cats/effect/Resource.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -138,6 +138,16 @@ sealed abstract class Resource[F[_], A] {
def flatMap[B](f: A => Resource[F, B]): Resource[F, B] =
Bind(this, f)

/**
* Direct implementation of the `map` operation which is otherwise
* available via the `cats.Monad` instance for `Resource[F, ?]`
*
* This allows IDEs which have issues with Partial Unification to
* see `map`.
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@alexandru alexandru Dec 3, 2018 •
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The reason for why this map is provided shouldn't be exposed in ScalaDoc, especially since now this implementation becomes the "source of truth" for Resource.

Just do something generic like ...

Given a mapping function, transforms the source.

This is the standard `Functor.map`.

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But I think we need another ScalaDoc comment, on Resource class, mentioning:

  1. -Ypartial-unification
  2. import cats.implicits._

... to unlock all available operations.

*/
def map[B](f: A => B)(implicit F: Applicative[F]): Resource[F, B] =
flatMap(a => Resource.pure[F, B](f(a)))

/**
* Given a `Resource`, possibly built by composing multiple
* `Resource`s monadically, returns the acquired resource, as well
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8 changes: 8 additions & 0 deletions laws/shared/src/test/scala/cats/effect/ResourceTests.scala
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Expand Up @@ -87,6 +87,13 @@ class ResourceTests extends BaseTestsSuite {
Resource.liftF(fa).use(IO.pure) <-> fa
}
}
testAsync("map should be the same as going via Monad") { implicit ec =>
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Instead of adding this test, a better idea would be to override map in the provided Monad instance.

val monad = implicitly[Monad[Resource[IO, ?]]]
check { fa: IO[String] =>
Resource.liftF(fa).map(_.toLowerCase).use(IO.pure) <->
monad.map(Resource.liftF(fa))(_.toLowerCase).use(IO.pure)
}
}

testAsync("allocated produces the same value as the resource") { implicit ec =>
check { resource: Resource[IO, Int] =>
Expand Down Expand Up @@ -117,4 +124,5 @@ class ResourceTests extends BaseTestsSuite {
val suspend = Resource.suspend[IO, Int](IO.raiseError(exception))
suspend.attempt.use(IO.pure).unsafeRunSync() shouldBe Left(exception)
}

}