/**
* Copyright (c) 2016-present, RxJava Contributors.
*
* 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 io.reactivex;
import io.reactivex.annotations.*;
/**
* Interface to map/wrap a downstream observer to an upstream observer.
*
* @param <Downstream> the value type of the downstream
* @param <Upstream> the value type of the upstream
*/
public interface ObservableOperator<Downstream, Upstream> {
/**
* Applies a function to the child Observer and returns a new parent Observer.
* @param observer the child Observer instance
* @return the parent Observer instance
* @throws Exception on failure
*/
@NonNull
Observer<? super Upstream> apply(@NonNull Observer<? super Downstream> observer) throws Exception;
}