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//-----------------------------------------------------------------------
// <copyright file="EmptyDictionary.cs" company="Outercurve Foundation">
// Copyright (c) Outercurve Foundation. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------
namespace DotNetOpenAuth.Messaging {
using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
/// <summary>
/// An empty dictionary. Useful for avoiding memory allocations in creating new dictionaries to represent empty ones.
/// </summary>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <typeparam name="TValue">The type of the value.</typeparam>
[Serializable]
internal class EmptyDictionary<TKey, TValue> : IDictionary<TKey, TValue> {
/// <summary>
/// The singleton instance of the empty dictionary.
/// </summary>
internal static readonly EmptyDictionary<TKey, TValue> Instance = new EmptyDictionary<TKey, TValue>();
/// <summary>
/// Prevents a default instance of the EmptyDictionary class from being created.
/// </summary>
private EmptyDictionary() {
}
/// <summary>
/// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <value></value>
/// <returns>
/// An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </returns>
public ICollection<TValue> Values {
get { return EmptyList<TValue>.Instance; }
}
/// <summary>
/// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <value></value>
/// <returns>
/// The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
public int Count {
get { return 0; }
}
/// <summary>
/// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </summary>
/// <value></value>
/// <returns>true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.
/// </returns>
public bool IsReadOnly {
get { return true; }
}
/// <summary>
/// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <value></value>
/// <returns>
/// An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </returns>
public ICollection<TKey> Keys {
get { return EmptyList<TKey>.Instance; }
}
/// <summary>
/// Gets or sets the value with the specified key.
/// </summary>
/// <param name="key">The key being read or written.</param>
/// <returns>Nothing. It always throws.</returns>
public TValue this[TKey key] {
get { throw new KeyNotFoundException(); }
set { throw new NotSupportedException(); }
}
/// <summary>
/// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <param name="key">The object to use as the key of the element to add.</param>
/// <param name="value">The object to use as the value of the element to add.</param>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="key"/> is null.
/// </exception>
/// <exception cref="T:System.ArgumentException">
/// An element with the same key already exists in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </exception>
/// <exception cref="T:System.NotSupportedException">
/// The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
/// </exception>
public void Add(TKey key, TValue value) {
throw new NotSupportedException();
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key.
/// </summary>
/// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</param>
/// <returns>
/// true if the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the key; otherwise, false.
/// </returns>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="key"/> is null.
/// </exception>
public bool ContainsKey(TKey key) {
return false;
}
/// <summary>
/// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <param name="key">The key of the element to remove.</param>
/// <returns>
/// true if the element is successfully removed; otherwise, false. This method also returns false if <paramref name="key"/> was not found in the original <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </returns>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="key"/> is null.
/// </exception>
/// <exception cref="T:System.NotSupportedException">
/// The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
/// </exception>
public bool Remove(TKey key) {
return false;
}
/// <summary>
/// Gets the value associated with the specified key.
/// </summary>
/// <param name="key">The key whose value to get.</param>
/// <param name="value">When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the type of the <paramref name="value"/> parameter. This parameter is passed uninitialized.</param>
/// <returns>
/// true if the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key; otherwise, false.
/// </returns>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="key"/> is null.
/// </exception>
public bool TryGetValue(TKey key, out TValue value) {
value = default(TValue);
return false;
}
#region ICollection<KeyValuePair<TKey,TValue>> Members
/// <summary>
/// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
/// <exception cref="T:System.NotSupportedException">
/// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </exception>
[SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes", Justification = "Code Contracts ccrewrite does this.")]
public void Add(KeyValuePair<TKey, TValue> item) {
throw new NotSupportedException();
}
/// <summary>
/// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <exception cref="T:System.NotSupportedException">
/// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </exception>
public void Clear() {
throw new NotSupportedException();
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
/// </summary>
/// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
/// <returns>
/// true if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false.
/// </returns>
public bool Contains(KeyValuePair<TKey, TValue> item) {
return false;
}
/// <summary>
/// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
/// </summary>
/// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.</param>
/// <param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="array"/> is null.
/// </exception>
/// <exception cref="T:System.ArgumentOutOfRangeException">
/// <paramref name="arrayIndex"/> is less than 0.
/// </exception>
/// <exception cref="T:System.ArgumentException">
/// <paramref name="array"/> is multidimensional.
/// -or-
/// <paramref name="arrayIndex"/> is equal to or greater than the length of <paramref name="array"/>.
/// -or-
/// The number of elements in the source <see cref="T:System.Collections.Generic.ICollection`1"/> is greater than the available space from <paramref name="arrayIndex"/> to the end of the destination <paramref name="array"/>.
/// -or-
/// Type cannot be cast automatically to the type of the destination <paramref name="array"/>.
/// </exception>
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) {
}
/// <summary>
/// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
/// <returns>
/// true if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
/// <exception cref="T:System.NotSupportedException">
/// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </exception>
public bool Remove(KeyValuePair<TKey, TValue> item) {
return false;
}
#endregion
#region IEnumerable<KeyValuePair<TKey,TValue>> Members
/// <summary>
/// Returns an enumerator that iterates through the collection.
/// </summary>
/// <returns>
/// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
/// </returns>
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() {
return Enumerable.Empty<KeyValuePair<TKey, TValue>>().GetEnumerator();
}
#endregion
#region IEnumerable Members
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
/// </returns>
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
return EmptyEnumerator.Instance;
}
#endregion
}
}
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