Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/ModelBinding/DictionaryHelpers.cs

@@ -0,0 +1,40 @@
+namespace System.Web.ModelBinding {
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+
+    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();
+        }
+
+    }
+}