mcs/class/referencesource/System.Web/Util/ReflectionUtil.cs

   1 //------------------------------------------------------------------------------
   2 // <copyright file="ReflectionUtil.cs" company="Microsoft">
   3 //     Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 //------------------------------------------------------------------------------
   6
   7 namespace System.Web.Util {
   8     using System;
   9     using System.Reflection;
  10     using System.Reflection.Emit;
  11     using System.Security.Permissions;
  12
  13     // Provides helper methods for performing reflection over managed objects.
  14
  15     [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]
  16     internal static class ReflectionUtil {
  17
  18         // Resets an object to its "default" state, e.g. where each instance field is given the value default(TField).
  19         public static void Reset<T>(T obj) where T : class {
  20             ResetUtil<T>.ResetFn(obj);
  21         }
  22
  23         private static class ResetUtil<T> where T : class {
  24             internal readonly static Action<T> ResetFn = CreateResetFn();
  25
  26             private static Action<T> CreateResetFn() {
  27                 Type targetType = typeof(T);
  28                 DynamicMethod dynamicMethod = CreateDynamicMethodWithAssert();
  29                 ILGenerator ilGen = dynamicMethod.GetILGenerator();
  30
  31                 // for each field in the target type, reset to default(TField)
  32                 FieldInfo[] allFields = targetType.GetFields(BindingFlags.Instance | BindingFlags.DeclaredOnly | BindingFlags.NonPublic | BindingFlags.Public);
  33                 foreach (FieldInfo fieldInfo in allFields) {
  34                     if (fieldInfo.IsInitOnly || fieldInfo.IsDefined(typeof(DoNotResetAttribute))) {
  35                         // This field is not eligible to be reset because it is marked readonly or [DoNotReset].
  36                         continue;
  37                     }
  38
  39                     // obj.field = default(TField);
  40                     // Opcodes.Initobj can be used for both value and reference types; see ECMA 335, Partition III, Sec. 4.5 "initobj"
  41                     // (ref: http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-335.pdf)
  42                     ilGen.Emit(OpCodes.Ldarg_0);
  43                     ilGen.Emit(OpCodes.Ldflda, fieldInfo);
  44                     ilGen.Emit(OpCodes.Initobj, fieldInfo.FieldType);
  45                 }
  46
  47                 ilGen.Emit(OpCodes.Ret);
  48                 // dynamicMethod = obj => {
  49                 //   obj.field1 = default(TField1);
  50                 //   obj.field2 = default(TField2);
  51                 //   ...
  52                 // };
  53                 return (Action<T>)dynamicMethod.CreateDelegate(typeof(Action<T>));
  54             }
  55
  56             [ReflectionPermission(SecurityAction.Assert, MemberAccess = true)] // needed to create a DynamicMethod inside the target type
  57             private static DynamicMethod CreateDynamicMethodWithAssert() {
  58                 Type targetType = typeof(T);
  59                 return new DynamicMethod(
  60                     name: "Reset-" + targetType.Name,
  61                     returnType: typeof(void),
  62                     parameterTypes: new Type[] { targetType },
  63                     owner: targetType,
  64                     skipVisibility: true);
  65             }
  66         }
  67
  68     }
  69 }