src/DotNetOpenAuth/Messaging/EmptyDictionary.cs

   1 //-----------------------------------------------------------------------
   2 // <copyright file="EmptyDictionary.cs" company="Andrew Arnott">
   3 //     Copyright (c) Andrew Arnott. All rights reserved.
   4 // </copyright>
   5 //-----------------------------------------------------------------------
   6
   7 namespace DotNetOpenAuth.Messaging {
   8         using System;
   9         using System.Collections.Generic;
  10         using System.Linq;
  11
  12         /// <summary>
  13         /// An empty dictionary.  Useful for avoiding memory allocations in creating new dictionaries to represent empty ones.
  14         /// </summary>
  15         /// <typeparam name="TKey">The type of the key.</typeparam>
  16         /// <typeparam name="TValue">The type of the value.</typeparam>
  17         internal class EmptyDictionary<TKey, TValue> : IDictionary<TKey, TValue> {
  18                 /// <summary>
  19                 /// The singleton instance of the empty dictionary.
  20                 /// </summary>
  21                 internal static readonly EmptyDictionary<TKey, TValue> Instance = new EmptyDictionary<TKey, TValue>();
  22
  23                 /// <summary>
  24                 /// Prevents a default instance of the EmptyDictionary class from being created.
  25                 /// </summary>
  26                 private EmptyDictionary() {
  27                 }
  28
  29                 /// <summary>
  30                 /// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
  31                 /// </summary>
  32                 /// <value></value>
  33                 /// <returns>
  34                 /// 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"/>.
  35                 /// </returns>
  36                 public ICollection<TValue> Values {
  37                         get { return EmptyList<TValue>.Instance; }
  38                 }
  39
  40                 /// <summary>
  41                 /// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
  42                 /// </summary>
  43                 /// <value></value>
  44                 /// <returns>
  45                 /// The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
  46                 /// </returns>
  47                 public int Count {
  48                         get { return 0; }
  49                 }
  50
  51                 /// <summary>
  52                 /// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
  53                 /// </summary>
  54                 /// <value></value>
  55                 /// <returns>true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.
  56                 /// </returns>
  57                 public bool IsReadOnly {
  58                         get { return true; }
  59                 }
  60
  61                 /// <summary>
  62                 /// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
  63                 /// </summary>
  64                 /// <value></value>
  65                 /// <returns>
  66                 /// 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"/>.
  67                 /// </returns>
  68                 public ICollection<TKey> Keys {
  69                         get { return EmptyList<TKey>.Instance; }
  70                 }
  71
  72                 /// <summary>
  73                 /// Gets or sets the value with the specified key.
  74                 /// </summary>
  75                 /// <param name="key">The key being read or written.</param>
  76                 public TValue this[TKey key] {
  77                         get { throw new KeyNotFoundException(); }
  78                         set { throw new NotSupportedException(); }
  79                 }
  80
  81                 /// <summary>
  82                 /// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
  83                 /// </summary>
  84                 /// <param name="key">The object to use as the key of the element to add.</param>
  85                 /// <param name="value">The object to use as the value of the element to add.</param>
  86                 /// <exception cref="T:System.ArgumentNullException">
  87                 ///     <paramref name="key"/> is null.
  88                 /// </exception>
  89                 /// <exception cref="T:System.ArgumentException">
  90                 /// An element with the same key already exists in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
  91                 /// </exception>
  92                 /// <exception cref="T:System.NotSupportedException">
  93                 /// The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
  94                 /// </exception>
  95                 public void Add(TKey key, TValue value) {
  96                         throw new NotSupportedException();
  97                 }
  98
  99                 /// <summary>
 100                 /// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key.
 101                 /// </summary>
 102                 /// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</param>
 103                 /// <returns>
 104                 /// true if the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the key; otherwise, false.
 105                 /// </returns>
 106                 /// <exception cref="T:System.ArgumentNullException">
 107                 ///     <paramref name="key"/> is null.
 108                 /// </exception>
 109                 public bool ContainsKey(TKey key) {
 110                         return false;
 111                 }
 112
 113                 /// <summary>
 114                 /// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
 115                 /// </summary>
 116                 /// <param name="key">The key of the element to remove.</param>
 117                 /// <returns>
 118                 /// 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"/>.
 119                 /// </returns>
 120                 /// <exception cref="T:System.ArgumentNullException">
 121                 ///     <paramref name="key"/> is null.
 122                 /// </exception>
 123                 /// <exception cref="T:System.NotSupportedException">
 124                 /// The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
 125                 /// </exception>
 126                 public bool Remove(TKey key) {
 127                         return false;
 128                 }
 129
 130                 /// <summary>
 131                 /// Gets the value associated with the specified key.
 132                 /// </summary>
 133                 /// <param name="key">The key whose value to get.</param>
 134                 /// <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>
 135                 /// <returns>
 136                 /// true if the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key; otherwise, false.
 137                 /// </returns>
 138                 /// <exception cref="T:System.ArgumentNullException">
 139                 ///     <paramref name="key"/> is null.
 140                 /// </exception>
 141                 public bool TryGetValue(TKey key, out TValue value) {
 142                         value = default(TValue);
 143                         return false;
 144                 }
 145
 146                 #region ICollection<KeyValuePair<TKey,TValue>> Members
 147
 148                 /// <summary>
 149                 /// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
 150                 /// </summary>
 151                 /// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
 152                 /// <exception cref="T:System.NotSupportedException">
 153                 /// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
 154                 /// </exception>
 155                 public void Add(KeyValuePair<TKey, TValue> item) {
 156                         throw new NotSupportedException();
 157                 }
 158
 159                 /// <summary>
 160                 /// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
 161                 /// </summary>
 162                 /// <exception cref="T:System.NotSupportedException">
 163                 /// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
 164                 /// </exception>
 165                 public void Clear() {
 166                         throw new NotSupportedException();
 167                 }
 168
 169                 /// <summary>
 170                 /// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
 171                 /// </summary>
 172                 /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
 173                 /// <returns>
 174                 /// true if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false.
 175                 /// </returns>
 176                 public bool Contains(KeyValuePair<TKey, TValue> item) {
 177                         return false;
 178                 }
 179
 180                 /// <summary>
 181                 /// 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.
 182                 /// </summary>
 183                 /// <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>
 184                 /// <param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param>
 185                 /// <exception cref="T:System.ArgumentNullException">
 186                 ///     <paramref name="array"/> is null.
 187                 /// </exception>
 188                 /// <exception cref="T:System.ArgumentOutOfRangeException">
 189                 ///     <paramref name="arrayIndex"/> is less than 0.
 190                 /// </exception>
 191                 /// <exception cref="T:System.ArgumentException">
 192                 ///     <paramref name="array"/> is multidimensional.
 193                 /// -or-
 194                 /// <paramref name="arrayIndex"/> is equal to or greater than the length of <paramref name="array"/>.
 195                 /// -or-
 196                 /// 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"/>.
 197                 /// -or-
 198                 /// Type <paramref name="T"/> cannot be cast automatically to the type of the destination <paramref name="array"/>.
 199                 /// </exception>
 200                 public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) {
 201                 }
 202
 203                 /// <summary>
 204                 /// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
 205                 /// </summary>
 206                 /// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
 207                 /// <returns>
 208                 /// 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"/>.
 209                 /// </returns>
 210                 /// <exception cref="T:System.NotSupportedException">
 211                 /// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
 212                 /// </exception>
 213                 public bool Remove(KeyValuePair<TKey, TValue> item) {
 214                         return false;
 215                 }
 216
 217                 #endregion
 218
 219                 #region IEnumerable<KeyValuePair<TKey,TValue>> Members
 220
 221                 /// <summary>
 222                 /// Returns an enumerator that iterates through the collection.
 223                 /// </summary>
 224                 /// <returns>
 225                 /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
 226                 /// </returns>
 227                 public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() {
 228                         return Enumerable.Empty<KeyValuePair<TKey, TValue>>().GetEnumerator();
 229                 }
 230
 231                 #endregion
 232
 233                 #region IEnumerable Members
 234
 235                 /// <summary>
 236                 /// Returns an enumerator that iterates through a collection.
 237                 /// </summary>
 238                 /// <returns>
 239                 /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
 240                 /// </returns>
 241                 System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
 242                         return EmptyEnumerator.Instance;
 243                 }
 244
 245                 #endregion
 246         }
 247 }