#region Apache License
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//
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// Licensed to the Apache Software Foundation (ASF) under one or more
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// contributor license agreements. See the NOTICE file distributed with
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// this work for additional information regarding copyright ownership.
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// The ASF licenses this file to you under the Apache License, Version 2.0
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// (the "License"); you may not use this file except in compliance with
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// the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#endregion
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using System;
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using System.Collections;
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namespace log4net.Util
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{
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/// <summary>
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/// An always empty <see cref="IDictionary"/>.
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/// </summary>
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/// <remarks>
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/// <para>
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/// A singleton implementation of the <see cref="IDictionary"/>
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/// interface that always represents an empty collection.
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/// </para>
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/// </remarks>
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/// <author>Nicko Cadell</author>
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/// <author>Gert Driesen</author>
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#if !NETCF
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[Serializable]
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#endif
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public sealed class EmptyDictionary : IDictionary
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{
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#region Private Instance Constructors
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/// <summary>
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/// Initializes a new instance of the <see cref="EmptyDictionary" /> class.
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/// </summary>
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/// <remarks>
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/// <para>
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/// Uses a private access modifier to enforce the singleton pattern.
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/// </para>
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/// </remarks>
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private EmptyDictionary()
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{
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}
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#endregion Private Instance Constructors
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#region Public Static Properties
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/// <summary>
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/// Gets the singleton instance of the <see cref="EmptyDictionary" />.
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/// </summary>
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/// <returns>The singleton instance of the <see cref="EmptyDictionary" />.</returns>
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/// <remarks>
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/// <para>
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/// Gets the singleton instance of the <see cref="EmptyDictionary" />.
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/// </para>
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/// </remarks>
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public static EmptyDictionary Instance
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{
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get { return s_instance; }
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}
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#endregion Public Static Properties
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#region Implementation of ICollection
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/// <summary>
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/// Copies the elements of the <see cref="ICollection"/> to an
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/// <see cref="Array"/>, starting at a particular Array index.
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/// </summary>
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/// <param name="array">The one-dimensional <see cref="Array"/>
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/// that is the destination of the elements copied from
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/// <see cref="ICollection"/>. The Array must have zero-based
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/// indexing.</param>
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/// <param name="index">The zero-based index in array at which
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/// copying begins.</param>
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/// <remarks>
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/// <para>
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/// As the collection is empty no values are copied into the array.
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/// </para>
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/// </remarks>
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public void CopyTo(System.Array array, int index)
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{
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// copy nothing
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}
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/// <summary>
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/// Gets a value indicating if access to the <see cref="ICollection"/> is synchronized (thread-safe).
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/// </summary>
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/// <value>
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/// <b>true</b> if access to the <see cref="ICollection"/> is synchronized (thread-safe); otherwise, <b>false</b>.
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/// </value>
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/// <remarks>
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/// <para>
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/// For the <see cref="EmptyCollection"/> this property is always <b>true</b>.
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/// </para>
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/// </remarks>
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public bool IsSynchronized
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{
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get { return true; }
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}
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/// <summary>
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/// Gets the number of elements contained in the <see cref="ICollection"/>
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/// </summary>
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/// <value>
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/// The number of elements contained in the <see cref="ICollection"/>.
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/// </value>
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/// <remarks>
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/// <para>
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/// As the collection is empty the <see cref="Count"/> is always <c>0</c>.
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/// </para>
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/// </remarks>
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public int Count
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{
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get { return 0; }
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}
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/// <summary>
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/// Gets an object that can be used to synchronize access to the <see cref="ICollection"/>.
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/// </summary>
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/// <value>
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/// An object that can be used to synchronize access to the <see cref="ICollection"/>.
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/// </value>
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/// <remarks>
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/// <para>
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/// As the collection is empty and thread safe and synchronized this instance is also
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/// the <see cref="SyncRoot"/> object.
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/// </para>
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/// </remarks>
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public object SyncRoot
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{
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get { return this; }
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}
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#endregion Implementation of ICollection
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#region Implementation of IEnumerable
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/// <summary>
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/// Returns an enumerator that can iterate through a collection.
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/// </summary>
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/// <returns>
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/// An <see cref="IEnumerator"/> that can be used to
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/// iterate through the collection.
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/// </returns>
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/// <remarks>
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/// <para>
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/// As the collection is empty a <see cref="NullEnumerator"/> is returned.
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/// </para>
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/// </remarks>
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IEnumerator IEnumerable.GetEnumerator()
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{
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return NullEnumerator.Instance;
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}
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#endregion Implementation of IEnumerable
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#region Implementation of IDictionary
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/// <summary>
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/// Adds an element with the provided key and value to the
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/// <see cref="EmptyDictionary" />.
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/// </summary>
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/// <param name="key">The <see cref="object" /> to use as the key of the element to add.</param>
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/// <param name="value">The <see cref="object" /> to use as the value of the element to add.</param>
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/// <remarks>
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/// <para>
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/// As the collection is empty no new values can be added. A <see cref="InvalidOperationException"/>
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/// is thrown if this method is called.
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/// </para>
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/// </remarks>
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/// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception>
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public void Add(object key, object value)
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{
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throw new InvalidOperationException();
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}
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/// <summary>
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/// Removes all elements from the <see cref="EmptyDictionary" />.
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/// </summary>
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/// <remarks>
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/// <para>
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/// As the collection is empty no values can be removed. A <see cref="InvalidOperationException"/>
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/// is thrown if this method is called.
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/// </para>
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/// </remarks>
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/// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception>
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public void Clear()
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{
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throw new InvalidOperationException();
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}
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/// <summary>
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/// Determines whether the <see cref="EmptyDictionary" /> contains an element
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/// with the specified key.
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/// </summary>
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/// <param name="key">The key to locate in the <see cref="EmptyDictionary" />.</param>
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/// <returns><c>false</c></returns>
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/// <remarks>
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/// <para>
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/// As the collection is empty the <see cref="Contains"/> method always returns <c>false</c>.
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/// </para>
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/// </remarks>
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public bool Contains(object key)
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{
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return false;
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}
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/// <summary>
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/// Returns an enumerator that can iterate through a collection.
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/// </summary>
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/// <returns>
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/// An <see cref="IEnumerator"/> that can be used to
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/// iterate through the collection.
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/// </returns>
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/// <remarks>
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/// <para>
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/// As the collection is empty a <see cref="NullEnumerator"/> is returned.
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/// </para>
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/// </remarks>
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public IDictionaryEnumerator GetEnumerator()
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{
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return NullDictionaryEnumerator.Instance;
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}
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/// <summary>
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/// Removes the element with the specified key from the <see cref="EmptyDictionary" />.
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/// </summary>
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/// <param name="key">The key of the element to remove.</param>
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/// <remarks>
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/// <para>
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/// As the collection is empty no values can be removed. A <see cref="InvalidOperationException"/>
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/// is thrown if this method is called.
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/// </para>
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/// </remarks>
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/// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception>
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public void Remove(object key)
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{
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throw new InvalidOperationException();
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}
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/// <summary>
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/// Gets a value indicating whether the <see cref="EmptyDictionary" /> has a fixed size.
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/// </summary>
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/// <value><c>true</c></value>
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/// <remarks>
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/// <para>
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/// As the collection is empty <see cref="IsFixedSize"/> always returns <c>true</c>.
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/// </para>
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/// </remarks>
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public bool IsFixedSize
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{
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get { return true; }
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}
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/// <summary>
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/// Gets a value indicating whether the <see cref="EmptyDictionary" /> is read-only.
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/// </summary>
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/// <value><c>true</c></value>
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/// <remarks>
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/// <para>
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/// As the collection is empty <see cref="IsReadOnly"/> always returns <c>true</c>.
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/// </para>
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/// </remarks>
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public bool IsReadOnly
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{
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get { return true; }
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}
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/// <summary>
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/// Gets an <see cref="ICollection" /> containing the keys of the <see cref="EmptyDictionary" />.
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/// </summary>
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/// <value>An <see cref="ICollection" /> containing the keys of the <see cref="EmptyDictionary" />.</value>
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/// <remarks>
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/// <para>
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/// As the collection is empty a <see cref="EmptyCollection"/> is returned.
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/// </para>
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/// </remarks>
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public System.Collections.ICollection Keys
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{
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get { return EmptyCollection.Instance; }
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}
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/// <summary>
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/// Gets an <see cref="ICollection" /> containing the values of the <see cref="EmptyDictionary" />.
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/// </summary>
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/// <value>An <see cref="ICollection" /> containing the values of the <see cref="EmptyDictionary" />.</value>
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/// <remarks>
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/// <para>
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/// As the collection is empty a <see cref="EmptyCollection"/> is returned.
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/// </para>
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/// </remarks>
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public System.Collections.ICollection Values
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{
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get { return EmptyCollection.Instance; }
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}
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/// <summary>
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/// Gets or sets the element with the specified key.
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/// </summary>
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/// <param name="key">The key of the element to get or set.</param>
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/// <value><c>null</c></value>
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/// <remarks>
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/// <para>
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/// As the collection is empty no values can be looked up or stored.
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/// If the index getter is called then <c>null</c> is returned.
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/// A <see cref="InvalidOperationException"/> is thrown if the setter is called.
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/// </para>
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/// </remarks>
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/// <exception cref="InvalidOperationException">This dictionary is always empty and cannot be modified.</exception>
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public object this[object key]
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{
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get { return null; }
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set { throw new InvalidOperationException(); }
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}
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#endregion Implementation of IDictionary
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#region Private Static Fields
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/// <summary>
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/// The singleton instance of the empty dictionary.
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/// </summary>
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private readonly static EmptyDictionary s_instance = new EmptyDictionary();
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#endregion Private Static Fields
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}
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}
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