Add Cats and ScalaCheck instances #1071
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kubukoz
reviewed
Oct 4, 2024
| @@ -21,4 +23,10 @@ final case class Kernel(toHeaders: Map[CIString, String]) { | |||
| object Kernel { | |||
| private[natchez] def fromJava(headers: util.Map[String, String]): Kernel = | |||
| apply(headers.asScala.map { case (k, v) => CIString(k) -> v }.toMap) | |||
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| implicit val kernelMonoid: Monoid[Kernel] = | |||
| Monoid.instance(Kernel(Map.empty), (a, b) => Kernel(a.toHeaders |+| b.toHeaders)) | |||
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issue: a.toHeaders is a Map[CIString, *], so its monoid will use the monoid of String to combine values under the same (case insensitive) key - it will concatenate them. I don't think these are safe semantics for this monoid.
scala-cli --toolkit typelevel:default
Welcome to Scala 3.5.0 (21.0.2, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
scala> import org.typelevel.ci.*, cats.*, cats.implicits.*
scala> Map(CIString("aaa") -> "hello") |+| Map(CIString("AAA") -> "goodbye")
val res0: Map[org.typelevel.ci.CIString, String] = Map(AAA -> hellogoodbye)I think the desired semantics would likely be to prefer RHS in case of conflict. So,
Suggested change
| Monoid.instance(Kernel(Map.empty), (a, b) => Kernel(a.toHeaders |+| b.toHeaders)) | |
| Monoid.instance(Kernel(Map.empty), (a, b) => Kernel(a.toHeaders ++ b.toHeaders)) |
and at this point I would suggest a test for the conflicting case, just to prevent accidents.
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Good catch. I'll update accordingly.
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I'd like to use these in a forthcoming PR to natchez-http4s, and I thought they might be useful generally.