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Cache List Monoid instance #4313

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Cache List Monoid instance #4313

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ee9d6ea
Cache List Monoid instance
TimWSpence Oct 5, 2022
421ccd0
Bincompat hacking
TimWSpence Oct 5, 2022
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7 changes: 6 additions & 1 deletion kernel/src/main/scala/cats/kernel/instances/ListInstances.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -29,8 +29,9 @@ import compat.scalaVersionSpecific._
trait ListInstances extends ListInstances1 {
implicit def catsKernelStdOrderForList[A: Order]: Order[List[A]] =
new ListOrder[A]

implicit def catsKernelStdMonoidForList[A]: Monoid[List[A]] =
new ListMonoid[A]
ListInstances.theListMonoidInstance.asInstanceOf[Monoid[List[A]]]
}

private[instances] trait ListInstances1 extends ListInstances2 {
Expand All @@ -46,6 +47,10 @@ private[instances] trait ListInstances2 {
new ListEq[A]
}

private[kernel] object ListInstances {
implicit private[this] val theListMonoidInstance: Monoid[List[Any]] = new ListMonoid[Any]
}

class ListOrder[A](implicit ev: Order[A]) extends Order[List[A]] {
def compare(xs: List[A], ys: List[A]): Int = {
@tailrec def loop(xs: List[A], ys: List[A]): Int =
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