content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.beam.sdk.state;
  
  /**
   * A {@link ReadableState} cell containing a set of elements.
   *
   * <p>Implementations of this form of state are expected to implement set operations such as {@link
   * #contains(Object)} efficiently, reading as little of the overall set as possible.
   *
   * @param <T> The type of elements in the set.
   */
  public interface SetState<T> extends GroupingState<T, Iterable<T>> {
    /**
     * Returns a {@link ReadableState} whose {@link #read} method will return true if this set
     * contains the specified element at the point when that {@link #read} call returns.
     */
    ReadableState<Boolean> contains(T t);
  
    /**
     * Ensures a value is a member of the set, returning {@code true} if it was added and {@code
     * false} otherwise.
     *
     * <p>Elements added will not be reflected in {@code OutputT} objects returned by previous calls
     * to {@link #read}.
     */
    ReadableState<Boolean> addIfAbsent(T t);
  
    /**
     * Removes the specified element from this set if it is present.
     *
     * <p>Changes will not be reflected in {@code OutputT} objects returned by previous calls to
     * {@link #read}.
     */
    void remove(T t);
  
    @Override
    SetState<T> readLater();
  }
  