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In Apply.semigroup test replace ListWrapper with Option #2827

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May 4, 2019
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In Apply.semigroup test replace ListWrapper with Option #2827

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In Apply.semigroup test replace ListWrapper with Option
kailuowang May 3, 2019
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kailuowang May 3, 2019
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kailuowang May 4, 2019
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7 changes: 7 additions & 0 deletions core/src/main/scala/cats/Apply.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,13 @@ trait Apply[F[_]] extends Functor[F] with InvariantSemigroupal[F] with ApplyArit
}

object Apply {

/**
* This semigroup uses a product operation to combine `F`s.
* If the `Apply[F].product` results in larger `F` (i.e. when `F` is a `List`),
* accumulative usage of this instance, such as `combineAll`, will result in
* `F`s with exponentially increasing sizes.
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Light copy editing (spans lines, so I couldn't GitHub it):

   * This semigroup uses a product operation to combine `F`s.
   * If the `Apply[F].product` results in larger `F` (i.e. when `F` is a `List`),
   * accumulative usage of this instance, such as `combineAll`, will result in
   * `F`s with exponentially increasing sizes.

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thanks!

*/
def semigroup[F[_], A](implicit f: Apply[F], sg: Semigroup[A]): Semigroup[F[A]] =
new ApplySemigroup[F, A](f, sg)
}
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6 changes: 3 additions & 3 deletions tests/src/test/scala/cats/tests/ApplicativeSuite.scala
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Expand Up @@ -46,10 +46,10 @@ class ApplicativeSuite extends CatsSuite {
}

{
implicit val listwrapperApply = ListWrapper.applyInstance
implicit val listwrapperSemigroup = Apply.semigroup[ListWrapper, Int]
checkAll("Apply[ListWrapper].semigroup", SemigroupTests[ListWrapper[Int]].semigroup)
val optionSemigroupFromApply = Apply.semigroup[Option, Int]
checkAll("Apply[Option].semigroup", SemigroupTests[Option[Int]](optionSemigroupFromApply).semigroup)
}

{
implicit val listwrapperApplicative = ListWrapper.applicative
implicit val listwrapperCoflatMap = Applicative.coflatMap[ListWrapper]
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