Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Entity/System/Data/Metadata/Edm/SafeLink.cs

@@ -0,0 +1,44 @@
+//---------------------------------------------------------------------
+// <copyright file="SafeLink.cs" company="Microsoft">
+//      Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//
+// @owner       [....]
+// @backupOwner [....]
+//---------------------------------------------------------------------using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Diagnostics;
+
+namespace System.Data.Metadata.Edm
+{
+    internal class SafeLink<TParent> where TParent : class
+    {
+        private TParent _value;
+        public TParent Value { get { return _value; } }
+
+
+        internal static IEnumerable<TChild> BindChildren<TChild>(TParent parent, Func<TChild, SafeLink<TParent>> getLink, IEnumerable<TChild> children)
+        {
+            
+            foreach (TChild child in children)
+            {
+                BindChild(parent, getLink, child);
+            }
+            return children;
+        }
+
+        internal static TChild BindChild<TChild>(TParent parent, Func<TChild, SafeLink<TParent>> getLink, TChild child)
+        {
+            SafeLink<TParent> link = getLink(child);
+
+            Debug.Assert(link._value == null || link._value == parent, "don't try to hook up the same child to a different parent");
+            // this is the good stuff.. 
+            // only this method can actually make the link since _value is a private
+            link._value = parent;
+
+            return child;
+        }
+    }
+}