Improved FallbackDictionary operations and allocations.

Author: tillig

src/Autofac/Util/FallbackDictionary.cs

@@ -55,7 +55,22 @@ public int Count
     {
         get
         {
-            return Keys.Count;
+            var count = _localValues.Count;
+
+            if (_parent.Count == 0)
+            {
+                return count;
+            }
+
+            foreach (var key in _parent.Keys)
+            {
+                if (!_localValues.ContainsKey(key))
+                {
+                    count++;
+                }
+            }
+
+            return count;
         }
     }
 
@@ -84,7 +99,7 @@ public bool IsReadOnly
     /// but it is guaranteed to be the same order as the corresponding values in the <see cref="ICollection{TKey}"/>
     /// returned by the <see cref="Values"/> property.
     /// </remarks>
-    public ICollection<TKey> Keys => GetOrderedKeysSnapshot();
+    public ICollection<TKey> Keys => GetMergedKeysSnapshot();
 
     /// <summary>
     /// Gets an <see cref="ICollection{TKey}"/> containing the values of the dictionary.
@@ -101,7 +116,7 @@ public ICollection<TValue> Values
     {
         get
         {
-            var keys = GetOrderedKeysSnapshot();
+            var keys = GetMergedKeysSnapshot();
             var values = new TValue[keys.Count];
             for (var i = 0; i < keys.Count; i++)
             {
@@ -222,7 +237,7 @@ public bool Contains(KeyValuePair<TKey, TValue> item)
     [SuppressMessage("CA1841", "CA1841", Justification = "False positive. This isn't a standard set of keys like other dictionaries.")]
     public bool ContainsKey(TKey key)
     {
-        return Keys.Contains(key);
+        return _localValues.ContainsKey(key) || _parent.ContainsKey(key);
     }
 
     /// <summary>
@@ -237,8 +252,26 @@ public bool ContainsKey(TKey key)
     /// </param>
     public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
     {
-        var resolved = (ICollection<KeyValuePair<TKey, TValue>>)new Dictionary<TKey, TValue>(this);
-        resolved.CopyTo(array, arrayIndex);
+        if (array == null)
+        {
+            throw new ArgumentNullException(nameof(array));
+        }
+
+        if (arrayIndex < 0 || arrayIndex > array.Length)
+        {
+            throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+        }
+
+        if (array.Length - arrayIndex < Count)
+        {
+            throw new ArgumentException(FallbackDictionaryResources.InsufficientArraySpace, nameof(array));
+        }
+
+        var index = arrayIndex;
+        foreach (var kvp in EnumerateKeyValuePairs())
+        {
+            array[index++] = kvp;
+        }
     }
 
     /// <summary>
@@ -249,10 +282,7 @@ public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
     /// </returns>
     public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
     {
-        foreach (var key in GetOrderedKeysSnapshot())
-        {
-            yield return new KeyValuePair<TKey, TValue>(key, this[key]);
-        }
+        return EnumerateKeyValuePairs().GetEnumerator();
     }
 
     /// <summary>
@@ -326,7 +356,7 @@ IEnumerator IEnumerable.GetEnumerator()
     /// Gets the list of correctly ordered unique keys from the local and parent dictionaries.
     /// </summary>
     /// <returns>A new list containing the ordered unique set of keys.</returns>
-    private List<TKey> GetOrderedKeysSnapshot()
+    private List<TKey> GetMergedKeysSnapshot()
     {
         var keys = new List<TKey>(_localValues.Count + _parent.Count);
         keys.AddRange(_localValues.Keys);
@@ -339,7 +369,24 @@ private List<TKey> GetOrderedKeysSnapshot()
             }
         }
 
-        keys.Sort();
         return keys;
     }
+
+    private IEnumerable<KeyValuePair<TKey, TValue>> EnumerateKeyValuePairs()
+    {
+        foreach (var kvp in _localValues)
+        {
+            yield return kvp;
+        }
+
+        foreach (var parentKvp in _parent)
+        {
+            if (_localValues.ContainsKey(parentKvp.Key))
+            {
+                continue;
+            }
+
+            yield return parentKvp;
+        }
+    }
 }

src/Autofac/Util/FallbackDictionaryResources.resx

@@ -120,4 +120,7 @@
   <data name="DuplicateItem" xml:space="preserve">
     <value>Item has already been added with key '{0}'.</value>
   </data>
+  <data name="InsufficientArraySpace" xml:space="preserve">
+    <value>The destination array does not have enough space to copy the items.</value>
+  </data>
 </root>