Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Entity/System/Data/SqlClient/SqlGen/SymbolUsageManager.cs

@@ -0,0 +1,78 @@
+//---------------------------------------------------------------------
+// <copyright file="SymbolUsageManager.cs" company="Microsoft">
+//      Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//
+// @owner  [....]
+//---------------------------------------------------------------------
+
+using System;
+using System.Collections.Generic;
+
+namespace System.Data.SqlClient.SqlGen
+{
+    /// <summary>
+    /// Used for wrapping a boolean value as an object.
+    /// </summary>
+    internal class BoolWrapper
+    {
+        internal bool Value {get; set;}
+
+        internal BoolWrapper()
+        {
+            this.Value = false;
+        }
+    }
+
+    /// <summary>
+    /// Tracks the usage of symbols. 
+    /// When registering a symbol with the usage manager if an input symbol is specified,
+    /// than the usage of the two is 'connected' - if one ever gets marked as used, 
+    /// the other one becomes 'used' too. 
+    /// </summary>
+    internal class SymbolUsageManager
+    {
+        private readonly Dictionary<Symbol, BoolWrapper> optionalColumnUsage = new Dictionary<Symbol, BoolWrapper>();
+
+        internal bool ContainsKey(Symbol key)
+        {
+            return optionalColumnUsage.ContainsKey(key);
+        }
+
+        internal bool TryGetValue(Symbol key, out bool value)
+        {
+            BoolWrapper wrapper;
+            if (optionalColumnUsage.TryGetValue(key, out wrapper))
+            {
+                value = wrapper.Value;
+                return true;
+            }
+
+            value = false;
+            return false;
+        }
+
+        internal void Add(Symbol sourceSymbol, Symbol symbolToAdd)
+        {
+            BoolWrapper wrapper;
+            if (sourceSymbol == null || !this.optionalColumnUsage.TryGetValue(sourceSymbol, out wrapper))
+            {
+                wrapper = new BoolWrapper();
+            }
+            this.optionalColumnUsage.Add(symbolToAdd, wrapper);
+        }
+
+        internal void MarkAsUsed(Symbol key)
+        {
+            if (optionalColumnUsage.ContainsKey(key))
+            {
+                optionalColumnUsage[key].Value = true;
+            }
+        }
+
+        internal bool IsUsed(Symbol key)
+        {
+            return optionalColumnUsage[key].Value;
+        }
+    }
+}