| #region Apache License |
| // |
| // 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. |
| // |
| #endregion |
| |
| using System; |
| using System.Collections; |
| |
| namespace log4net.Util |
| { |
| /// <summary> |
| /// An always empty <see cref="IEnumerator"/>. |
| /// </summary> |
| /// <remarks> |
| /// <para> |
| /// A singleton implementation of the <see cref="IEnumerator"/> over a collection |
| /// that is empty and not modifiable. |
| /// </para> |
| /// </remarks> |
| /// <author>Nicko Cadell</author> |
| /// <author>Gert Driesen</author> |
| public sealed class NullEnumerator : IEnumerator |
| { |
| #region Private Instance Constructors |
| |
| /// <summary> |
| /// Initializes a new instance of the <see cref="NullEnumerator" /> class. |
| /// </summary> |
| /// <remarks> |
| /// <para> |
| /// Uses a private access modifier to enforce the singleton pattern. |
| /// </para> |
| /// </remarks> |
| private NullEnumerator() |
| { |
| } |
| |
| #endregion Private Instance Constructors |
| |
| #region Public Static Properties |
| |
| /// <summary> |
| /// Get the singleton instance of the <see cref="NullEnumerator" />. |
| /// </summary> |
| /// <returns>The singleton instance of the <see cref="NullEnumerator" />.</returns> |
| /// <remarks> |
| /// <para> |
| /// Gets the singleton instance of the <see cref="NullEnumerator" />. |
| /// </para> |
| /// </remarks> |
| public static NullEnumerator Instance |
| { |
| get { return s_instance; } |
| } |
| |
| #endregion Public Static Properties |
| |
| #region Implementation of IEnumerator |
| |
| /// <summary> |
| /// Gets the current object from the enumerator. |
| /// </summary> |
| /// <remarks> |
| /// Throws an <see cref="InvalidOperationException" /> because the |
| /// <see cref="NullDictionaryEnumerator" /> never has a current value. |
| /// </remarks> |
| /// <remarks> |
| /// <para> |
| /// As the enumerator is over an empty collection its <see cref="Current"/> |
| /// value cannot be moved over a valid position, therefore <see cref="Current"/> |
| /// will throw an <see cref="InvalidOperationException"/>. |
| /// </para> |
| /// </remarks> |
| /// <exception cref="InvalidOperationException">The collection is empty and <see cref="Current"/> |
| /// cannot be positioned over a valid location.</exception> |
| public object Current |
| { |
| get { throw new InvalidOperationException(); } |
| } |
| |
| /// <summary> |
| /// Test if the enumerator can advance, if so advance |
| /// </summary> |
| /// <returns><c>false</c> as the <see cref="NullEnumerator" /> cannot advance.</returns> |
| /// <remarks> |
| /// <para> |
| /// As the enumerator is over an empty collection its <see cref="Current"/> |
| /// value cannot be moved over a valid position, therefore <see cref="MoveNext"/> |
| /// will always return <c>false</c>. |
| /// </para> |
| /// </remarks> |
| public bool MoveNext() |
| { |
| return false; |
| } |
| |
| /// <summary> |
| /// Resets the enumerator back to the start. |
| /// </summary> |
| /// <remarks> |
| /// <para> |
| /// As the enumerator is over an empty collection <see cref="Reset"/> does nothing. |
| /// </para> |
| /// </remarks> |
| public void Reset() |
| { |
| } |
| |
| #endregion Implementation of IEnumerator |
| |
| #region Private Static Fields |
| |
| /// <summary> |
| /// The singleton instance of the <see cref="NullEnumerator" />. |
| /// </summary> |
| private static readonly NullEnumerator s_instance = new NullEnumerator(); |
| |
| #endregion Private Static Fields |
| } |
| } |