| #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="IDictionary"/>. |
| /// </summary> |
| /// <remarks> |
| /// <para> |
| /// A singleton implementation of the <see cref="IDictionary"/> |
| /// interface that always represents an empty collection. |
| /// </para> |
| /// </remarks> |
| /// <author>Nicko Cadell</author> |
| /// <author>Gert Driesen</author> |
| #if !NETCF |
| [Serializable] |
| #endif |
| public sealed class EmptyDictionary : IDictionary |
| { |
| #region Private Instance Constructors |
| |
| /// <summary> |
| /// Initializes a new instance of the <see cref="EmptyDictionary" /> class. |
| /// </summary> |
| /// <remarks> |
| /// <para> |
| /// Uses a private access modifier to enforce the singleton pattern. |
| /// </para> |
| /// </remarks> |
| private EmptyDictionary() |
| { |
| } |
| |
| #endregion Private Instance Constructors |
| |
| #region Public Static Properties |
| |
| /// <summary> |
| /// Gets the singleton instance of the <see cref="EmptyDictionary" />. |
| /// </summary> |
| /// <returns>The singleton instance of the <see cref="EmptyDictionary" />.</returns> |
| /// <remarks> |
| /// <para> |
| /// Gets the singleton instance of the <see cref="EmptyDictionary" />. |
| /// </para> |
| /// </remarks> |
| public static EmptyDictionary Instance |
| { |
| get { return s_instance; } |
| } |
| |
| #endregion Public Static Properties |
| |
| #region Implementation of ICollection |
| |
| /// <summary> |
| /// Copies the elements of the <see cref="ICollection"/> to an |
| /// <see cref="Array"/>, starting at a particular Array index. |
| /// </summary> |
| /// <param name="array">The one-dimensional <see cref="Array"/> |
| /// that is the destination of the elements copied from |
| /// <see cref="ICollection"/>. The Array must have zero-based |
| /// indexing.</param> |
| /// <param name="index">The zero-based index in array at which |
| /// copying begins.</param> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty no values are copied into the array. |
| /// </para> |
| /// </remarks> |
| public void CopyTo(System.Array array, int index) |
| { |
| // copy nothing |
| } |
| |
| /// <summary> |
| /// Gets a value indicating if access to the <see cref="ICollection"/> is synchronized (thread-safe). |
| /// </summary> |
| /// <value> |
| /// <b>true</b> if access to the <see cref="ICollection"/> is synchronized (thread-safe); otherwise, <b>false</b>. |
| /// </value> |
| /// <remarks> |
| /// <para> |
| /// For the <see cref="EmptyCollection"/> this property is always <b>true</b>. |
| /// </para> |
| /// </remarks> |
| public bool IsSynchronized |
| { |
| get { return true; } |
| } |
| |
| /// <summary> |
| /// Gets the number of elements contained in the <see cref="ICollection"/> |
| /// </summary> |
| /// <value> |
| /// The number of elements contained in the <see cref="ICollection"/>. |
| /// </value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty the <see cref="Count"/> is always <c>0</c>. |
| /// </para> |
| /// </remarks> |
| public int Count |
| { |
| get { return 0; } |
| } |
| |
| /// <summary> |
| /// Gets an object that can be used to synchronize access to the <see cref="ICollection"/>. |
| /// </summary> |
| /// <value> |
| /// An object that can be used to synchronize access to the <see cref="ICollection"/>. |
| /// </value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty and thread safe and synchronized this instance is also |
| /// the <see cref="SyncRoot"/> object. |
| /// </para> |
| /// </remarks> |
| public object SyncRoot |
| { |
| get { return this; } |
| } |
| |
| #endregion Implementation of ICollection |
| |
| #region Implementation of IEnumerable |
| |
| /// <summary> |
| /// Returns an enumerator that can iterate through a collection. |
| /// </summary> |
| /// <returns> |
| /// An <see cref="IEnumerator"/> that can be used to |
| /// iterate through the collection. |
| /// </returns> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty a <see cref="NullEnumerator"/> is returned. |
| /// </para> |
| /// </remarks> |
| IEnumerator IEnumerable.GetEnumerator() |
| { |
| return NullEnumerator.Instance; |
| } |
| |
| #endregion Implementation of IEnumerable |
| |
| #region Implementation of IDictionary |
| |
| /// <summary> |
| /// Adds an element with the provided key and value to the |
| /// <see cref="EmptyDictionary" />. |
| /// </summary> |
| /// <param name="key">The <see cref="object" /> to use as the key of the element to add.</param> |
| /// <param name="value">The <see cref="object" /> to use as the value of the element to add.</param> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty no new values can be added. A <see cref="InvalidOperationException"/> |
| /// is thrown if this method is called. |
| /// </para> |
| /// </remarks> |
| /// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception> |
| public void Add(object key, object value) |
| { |
| throw new InvalidOperationException(); |
| } |
| |
| /// <summary> |
| /// Removes all elements from the <see cref="EmptyDictionary" />. |
| /// </summary> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty no values can be removed. A <see cref="InvalidOperationException"/> |
| /// is thrown if this method is called. |
| /// </para> |
| /// </remarks> |
| /// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception> |
| public void Clear() |
| { |
| throw new InvalidOperationException(); |
| } |
| |
| /// <summary> |
| /// Determines whether the <see cref="EmptyDictionary" /> contains an element |
| /// with the specified key. |
| /// </summary> |
| /// <param name="key">The key to locate in the <see cref="EmptyDictionary" />.</param> |
| /// <returns><c>false</c></returns> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty the <see cref="Contains"/> method always returns <c>false</c>. |
| /// </para> |
| /// </remarks> |
| public bool Contains(object key) |
| { |
| return false; |
| } |
| |
| /// <summary> |
| /// Returns an enumerator that can iterate through a collection. |
| /// </summary> |
| /// <returns> |
| /// An <see cref="IEnumerator"/> that can be used to |
| /// iterate through the collection. |
| /// </returns> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty a <see cref="NullEnumerator"/> is returned. |
| /// </para> |
| /// </remarks> |
| public IDictionaryEnumerator GetEnumerator() |
| { |
| return NullDictionaryEnumerator.Instance; |
| } |
| |
| /// <summary> |
| /// Removes the element with the specified key from the <see cref="EmptyDictionary" />. |
| /// </summary> |
| /// <param name="key">The key of the element to remove.</param> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty no values can be removed. A <see cref="InvalidOperationException"/> |
| /// is thrown if this method is called. |
| /// </para> |
| /// </remarks> |
| /// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception> |
| public void Remove(object key) |
| { |
| throw new InvalidOperationException(); |
| } |
| |
| /// <summary> |
| /// Gets a value indicating whether the <see cref="EmptyDictionary" /> has a fixed size. |
| /// </summary> |
| /// <value><c>true</c></value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty <see cref="IsFixedSize"/> always returns <c>true</c>. |
| /// </para> |
| /// </remarks> |
| public bool IsFixedSize |
| { |
| get { return true; } |
| } |
| |
| /// <summary> |
| /// Gets a value indicating whether the <see cref="EmptyDictionary" /> is read-only. |
| /// </summary> |
| /// <value><c>true</c></value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty <see cref="IsReadOnly"/> always returns <c>true</c>. |
| /// </para> |
| /// </remarks> |
| public bool IsReadOnly |
| { |
| get { return true; } |
| } |
| |
| /// <summary> |
| /// Gets an <see cref="ICollection" /> containing the keys of the <see cref="EmptyDictionary" />. |
| /// </summary> |
| /// <value>An <see cref="ICollection" /> containing the keys of the <see cref="EmptyDictionary" />.</value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty a <see cref="EmptyCollection"/> is returned. |
| /// </para> |
| /// </remarks> |
| public System.Collections.ICollection Keys |
| { |
| get { return EmptyCollection.Instance; } |
| } |
| |
| /// <summary> |
| /// Gets an <see cref="ICollection" /> containing the values of the <see cref="EmptyDictionary" />. |
| /// </summary> |
| /// <value>An <see cref="ICollection" /> containing the values of the <see cref="EmptyDictionary" />.</value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty a <see cref="EmptyCollection"/> is returned. |
| /// </para> |
| /// </remarks> |
| public System.Collections.ICollection Values |
| { |
| get { return EmptyCollection.Instance; } |
| } |
| |
| /// <summary> |
| /// Gets or sets the element with the specified key. |
| /// </summary> |
| /// <param name="key">The key of the element to get or set.</param> |
| /// <value><c>null</c></value> |
| /// <remarks> |
| /// <para> |
| /// As the collection is empty no values can be looked up or stored. |
| /// If the index getter is called then <c>null</c> is returned. |
| /// A <see cref="InvalidOperationException"/> is thrown if the setter is called. |
| /// </para> |
| /// </remarks> |
| /// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception> |
| public object this[object key] |
| { |
| get { return null; } |
| set { throw new InvalidOperationException(); } |
| } |
| |
| #endregion Implementation of IDictionary |
| |
| #region Private Static Fields |
| |
| /// <summary> |
| /// The singleton instance of the empty dictionary. |
| /// </summary> |
| private readonly static EmptyDictionary s_instance = new EmptyDictionary(); |
| |
| #endregion Private Static Fields |
| } |
| } |