Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

external/aspnetwebstack/src/System.Web.Mvc/DictionaryHelpers.cs

@@ -0,0 +1,58 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Linq;
+
+namespace System.Web.Mvc
+{
+    internal static class DictionaryHelpers
+    {
+        public static IEnumerable<KeyValuePair<string, TValue>> FindKeysWithPrefix<TValue>(IDictionary<string, TValue> dictionary, string prefix)
+        {
+            TValue exactMatchValue;
+            if (dictionary.TryGetValue(prefix, out exactMatchValue))
+            {
+                yield return new KeyValuePair<string, TValue>(prefix, exactMatchValue);
+            }
+
+            foreach (var entry in dictionary)
+            {
+                string key = entry.Key;
+
+                if (key.Length <= prefix.Length)
+                {
+                    continue;
+                }
+
+                if (!key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
+                {
+                    continue;
+                }
+
+                char charAfterPrefix = key[prefix.Length];
+                switch (charAfterPrefix)
+                {
+                    case '[':
+                    case '.':
+                        yield return entry;
+                        break;
+                }
+            }
+        }
+
+        public static bool DoesAnyKeyHavePrefix<TValue>(IDictionary<string, TValue> dictionary, string prefix)
+        {
+            return FindKeysWithPrefix(dictionary, prefix).Any();
+        }
+
+        public static TValue GetOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> dict, TKey key, TValue @default)
+        {
+            TValue value;
+            if (dict.TryGetValue(key, out value))
+            {
+                return value;
+            }
+            return @default;
+        }
+    }
+}