尝试使用 Cats Effect Ref monad 以功能方式实现缓存。
为什么内部 Ref 没有按预期设置?
import cats.effect.kernel.Ref
import cats.effect.{IO, IOApp}
object SomeMain extends IOApp.Simple {
val cache: IO[Ref[IO, Option[String]]] = Ref.of[IO, Option[String]](None)
override def run: IO[Unit] = {
val checkValueBeforeSet = cache.flatMap(ref => ref.get.flatMap {
case Some(v) => IO(println(v))
case None => IO(println("as expected no value yet"))
})
val doSetAction = cache.flatMap(ref => ref.set(Some("abc"))).map(_ => println("set action done"))
val checkValueAfterSet = cache.flatMap(ref => ref.get.flatMap {
case Some(v) => IO(println(v))
case None => IO(println("unexpected still no value set!"))
})
for {
_ <- checkValueBeforeSet
_ <- doSetAction
_ <- checkValueAfterSet
} yield IO()
}
}
输出:
as expected no value yet
set action done
unexpected still no value set!