decrel.reify.Cache.scala Maven / Gradle / Ivy

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/*
 * Copyright (c) 2022 Haemin Yoo
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

package decrel.reify

import decrel.Relation
import izumi.reflect.Tag

/**
 * Simple cache implementation that is reusable across various integrations
 */
final case class Cache(
  entries: Map[Cache.Key[?, ?, ?], Cache.Entry[?, ?, ?]]
) {

  def add[Rel, A, B](relation: Rel & Relation[A, B], key: A, value: B)(implicit
    tag: Tag[Rel]
  ): Cache = {
    val k = Cache.Key(relation, Tag[Rel], key)
    new Cache(entries + (k -> Cache.Entry(k, value)))
  }

}

object Cache {

  // TODO see if there's a way to allow customizing the underlying Map
  val empty: Cache = Cache(Map.empty)

  final case class Key[Rel, A, B](
    relation: Rel & Relation[A, B],
    tag: Tag[Rel],
    key: A
  ) {
    type R      = Rel
    type RRel   = Rel & Relation[A, B]
    type Input  = A
    type Result = B

    private[decrel] def _relation: RRel                                    = relation
    private[decrel] def _key: Input                                        = key
    private[decrel] def relationEv: <:<[RRel, R & Relation[Input, Result]] = implicitly
  }

  final case class Entry[Rel, A, B](
    key: Key[Rel, A, B],
    value: B
  ) {
    type Result = B

    private[decrel] def _value: Result                   = value
    private[decrel] def valueEv: <:<[Result, key.Result] = implicitly
  }

}