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//------------------------------------------------------------------------------
// <copyright file="ReflectionUtil.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
namespace System.Web.Util {
using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Security.Permissions;
// Provides helper methods for performing reflection over managed objects.
[SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]
internal static class ReflectionUtil {
// Resets an object to its "default" state, e.g. where each instance field is given the value default(TField).
public static void Reset<T>(T obj) where T : class {
ResetUtil<T>.ResetFn(obj);
}
private static class ResetUtil<T> where T : class {
internal readonly static Action<T> ResetFn = CreateResetFn();
private static Action<T> CreateResetFn() {
Type targetType = typeof(T);
DynamicMethod dynamicMethod = CreateDynamicMethodWithAssert();
ILGenerator ilGen = dynamicMethod.GetILGenerator();
// for each field in the target type, reset to default(TField)
FieldInfo[] allFields = targetType.GetFields(BindingFlags.Instance | BindingFlags.DeclaredOnly | BindingFlags.NonPublic | BindingFlags.Public);
foreach (FieldInfo fieldInfo in allFields) {
if (fieldInfo.IsInitOnly || fieldInfo.IsDefined(typeof(DoNotResetAttribute))) {
// This field is not eligible to be reset because it is marked readonly or [DoNotReset].
continue;
}
// obj.field = default(TField);
// Opcodes.Initobj can be used for both value and reference types; see ECMA 335, Partition III, Sec. 4.5 "initobj"
// (ref: http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-335.pdf)
ilGen.Emit(OpCodes.Ldarg_0);
ilGen.Emit(OpCodes.Ldflda, fieldInfo);
ilGen.Emit(OpCodes.Initobj, fieldInfo.FieldType);
}
ilGen.Emit(OpCodes.Ret);
// dynamicMethod = obj => {
// obj.field1 = default(TField1);
// obj.field2 = default(TField2);
// ...
// };
return (Action<T>)dynamicMethod.CreateDelegate(typeof(Action<T>));
}
[ReflectionPermission(SecurityAction.Assert, MemberAccess = true)] // needed to create a DynamicMethod inside the target type
private static DynamicMethod CreateDynamicMethodWithAssert() {
Type targetType = typeof(T);
return new DynamicMethod(
name: "Reset-" + targetType.Name,
returnType: typeof(void),
parameterTypes: new Type[] { targetType },
owner: targetType,
skipVisibility: true);
}
}
}
}
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