Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

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+//---------------------------------------------------------------------
+// <copyright file="SymbolTable.cs" company="Microsoft">
+//      Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//
+// @owner  [....]
+// @backupOwner [....]
+//---------------------------------------------------------------------
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Text;
+using System.Data.SqlClient;
+using System.Data.Metadata.Edm;
+using System.Data.Common.CommandTrees;
+
+namespace System.Data.SqlClient.SqlGen
+{
+    /// <summary>
+    /// The symbol table is quite primitive - it is a stack with a new entry for
+    /// each scope.  Lookups search from the top of the stack to the bottom, until
+    /// an entry is found.
+    /// 
+    /// The symbols are of the following kinds
+    /// <list type="bullet">
+    /// <item><see cref="Symbol"/> represents tables (extents/nested selects/unnests)</item>
+    /// <item><see cref="JoinSymbol"/> represents Join nodes</item>
+    /// <item><see cref="Symbol"/> columns.</item>
+    /// </list>
+    /// 
+    /// Symbols represent names <see cref="SqlGenerator.Visit(DbVariableReferenceExpression)"/> to be resolved, 
+    /// or things to be renamed.
+    /// </summary>
+    internal sealed class SymbolTable
+    {
+        private List<Dictionary<string, Symbol>> symbols = new List<Dictionary<string, Symbol>>();
+
+        internal void EnterScope()
+        {
+            symbols.Add(new Dictionary<string, Symbol>(StringComparer.OrdinalIgnoreCase));
+        }
+
+        internal void ExitScope()
+        {
+            symbols.RemoveAt(symbols.Count - 1);
+        }
+
+        internal void Add(string name, Symbol value)
+        {
+            symbols[symbols.Count - 1][name] = value;
+        }
+
+        internal Symbol Lookup(string name)
+        {
+            for (int i = symbols.Count - 1; i >= 0; --i)
+            {
+                if (symbols[i].ContainsKey(name))
+                {
+                    return symbols[i][name];
+                }
+            }
+
+            return null;
+        }
+    }
+}