mcs/class/referencesource/System.Data.Entity/System/Data/Objects/ELinq/ExpressionVisitorHelpers.cs

   1 //---------------------------------------------------------------------
   2 // <copyright file="ExpressionVisitorHelper.cs" company="Microsoft">
   3 //      Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 //
   6 // @owner  Microsoft
   7 //---------------------------------------------------------------------
   8
   9 namespace System.Linq.Expressions.Internal
  10 {
  11     using System.Collections.Generic;
  12     using System.Collections.ObjectModel;
  13     using System.Data;
  14
  15     // Because we are using the source file for ExpressionVistor from System.Core
  16     // we need to add code to facilitate some external calls that ExpressionVisitor makes.
  17     // The classes in this file do that.
  18
  19     internal static class Error
  20     {
  21         internal static Exception UnhandledExpressionType(ExpressionType expressionType)
  22         {
  23             return EntityUtil.NotSupported(System.Data.Entity.Strings.ELinq_UnhandledExpressionType(expressionType));
  24         }
  25
  26         internal static Exception UnhandledBindingType(MemberBindingType memberBindingType)
  27         {
  28             return EntityUtil.NotSupported(System.Data.Entity.Strings.ELinq_UnhandledBindingType(memberBindingType));
  29         }
  30     }
  31
  32     internal static class ReadOnlyCollectionExtensions
  33     {
  34         internal static ReadOnlyCollection<T> ToReadOnlyCollection<T>(this IEnumerable<T> sequence)
  35         {
  36             if (sequence == null)
  37                 return DefaultReadOnlyCollection<T>.Empty;
  38             ReadOnlyCollection<T> col = sequence as ReadOnlyCollection<T>;
  39             if (col != null)
  40                 return col;
  41             return new ReadOnlyCollection<T>(sequence.ToArray());
  42         }
  43         private static class DefaultReadOnlyCollection<T>
  44         {
  45             private static ReadOnlyCollection<T> _defaultCollection;
  46             internal static ReadOnlyCollection<T> Empty
  47             {
  48                 get
  49                 {
  50                     if (_defaultCollection == null)
  51                         _defaultCollection = new ReadOnlyCollection<T>(new T[] { });
  52                     return _defaultCollection;
  53                 }
  54             }
  55         }
  56     }
  57 }