monix.reactive.internal.operators.DistinctUntilChangedOperator.scala Maven / Gradle / Ivy

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/*
 * Copyright (c) 2014-2016 by its authors. Some rights reserved.
 * See the project homepage at: https://monix.io
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package monix.reactive.internal.operators

import monix.execution.Ack.Continue
import monix.reactive.observables.ObservableLike
import ObservableLike.Operator
import monix.reactive.observers.Subscriber

private[reactive] final
class DistinctUntilChangedOperator[A] extends Operator[A,A] {

  def apply(out: Subscriber[A]): Subscriber[A] =
    new Subscriber[A] {
      implicit val scheduler = out.scheduler
      private[this] var isFirst = true
      private[this] var lastElem: A = _

      def onNext(elem: A) = {
        if (isFirst) {
          lastElem = elem
          isFirst = false
          out.onNext(elem)
        }
        else if (lastElem != elem) {
          lastElem = elem
          out.onNext(elem)
        }
        else
          Continue
      }

      def onError(ex: Throwable): Unit = out.onError(ex)
      def onComplete(): Unit = out.onComplete()
    }
}