System.Reflection.Emit：ref struct 的字段或属性

Question

对于以下接口和结构：

internal interface IRecord<T> where T : struct
{
    ref T Values { get; }
}

public struct Entity
{
    public int Field1;
    ...
}

我想通过反射获得以下 lambda 表达式：

Expression<Func<IRecord<Entity>, int>> getter = x => x.Values.Field1;
Expression<Action<IRecord<Entity>, int>> setter = (x, value) => x.Values.Field1 = value;

不幸的是，这不能编译： cs8153: an expression tree lambda may not contain a call to a method, property, or indexer that returns by reference 。 似乎通过反射不支持获取ref struct任何成员。

所以我必须去System.Reflection.Emit生成以下访问器类：

public static class Accessor
{
    public static int GetField1(IRecord<Entity> record) => record.Values.Field1;
    public static void SetField1(IRecord<Entity> record, int value) => record.Values.Field1 = value;
    ...
}

并通过反射得到以下 lambda 表达式：

Expression<Func<IRecord<Entity>, int>> getter = x => Accessor.GetField1(x);
Expression<Action<IRecord<Entity>, int>> setter = (x, value) => Accessor.SetField1(x, value);

这是我使用System.Reflection.Emit生成Accessor类的代码：

private static readonly ModuleBuilder ModuleBuilder = GetModuleBuilder();

private static ModuleBuilder GetModuleBuilder()
{
    AssemblyName assemblyName = new AssemblyName("AccessTypeBuilder");
    AssemblyBuilder assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
    ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("Module");
    return moduleBuilder;
}

public static Type BuildAccessorType(Type fieldValuesType)
{
    TypeBuilder typeBuilder = ModuleBuilder.DefineType("Accessor", TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.Sealed, typeof(object));
    BuildAccessor(typeBuilder, typeof(Entity), "Field1", typeof(int));
    return typeBuilder.CreateType();
}

private static void BuildAccessor(TypeBuilder typeBuilder, Type fieldValuesType, string fieldName, Type dataType)
{
    typeBuilder.DefineGetter(fieldValuesType, $"Get{fieldName}", dataType, fieldName);
    typeBuilder.DefineSetter(fieldValuesType, $"Set{fieldName}", dataType, fieldName);
}

private static void DefineField(this TypeBuilder typeBuilder, Type dataType, string fieldName)
{
    typeBuilder.DefineField(fieldName, dataType, FieldAttributes.Public);
}

private static Type RecordType(this Type fieldValuesType)
{
    return typeof(IRecord<>).MakeGenericType(fieldValuesType);
}

private static MethodInfo FieldValues(this Type fieldValuesType)
{
    var recordType = fieldValuesType.RecordType();
    var property = recordType.GetProperty(nameof(IRecord<int>.Values));
    return property.GetMethod;
}

private static FieldInfo Field(this Type fieldValuesType, string fieldName) => fieldValuesType.GetField(fieldName, BindingFlags.Public | BindingFlags.Instance);

private static void DefineGetter(this TypeBuilder typeBuilder, Type fieldValuesType, string methodName, Type dataType, string fieldName)
{
    var method = typeBuilder.DefineMethod(methodName, MethodAttributes.Public | MethodAttributes.Static, dataType, new Type[] { fieldValuesType.RecordType() });
    var methodBody = method.GetILGenerator();
    methodBody.EmitGetter(fieldValuesType, fieldName);
}

private static void EmitGetter(this ILGenerator methodBody, Type fieldValuesType, string fieldName)
{
    methodBody.Emit(OpCodes.Ldarg_0);
    methodBody.Emit(OpCodes.Callvirt, fieldValuesType.FieldValues());
    methodBody.Emit(OpCodes.Ldfld, fieldValuesType.Field(fieldName));
    methodBody.Emit(OpCodes.Stloc_0);
    methodBody.Emit(OpCodes.Ldloc_0);
    methodBody.Emit(OpCodes.Ret);
}

private static void DefineSetter(this TypeBuilder typeBuilder, Type fieldValuesType, string methodName, Type dataType, string fieldName)
{
    var method = typeBuilder.DefineMethod(methodName, MethodAttributes.Public | MethodAttributes.Static, typeof(void), new Type[] { fieldValuesType.RecordType(), dataType });
    var methodBody = method.GetILGenerator();
    methodBody.EmitSetter(fieldValuesType, fieldName);
}

private static void EmitSetter(this ILGenerator methodBody, Type fieldValuesType, string fieldName)
{
    methodBody.Emit(OpCodes.Nop);
    methodBody.Emit(OpCodes.Ldarg_0);
    methodBody.Emit(OpCodes.Callvirt, fieldValuesType.FieldValues());
    methodBody.Emit(OpCodes.Ldarg_1);
    methodBody.Emit(OpCodes.Stfld, fieldValuesType.Field(fieldName));
    methodBody.Emit(OpCodes.Ret);
}

使用生成的Accessor类时，我收到InvalidProgramException: Common Language Runtime detected an invalid program. 调用生成的 getter 时； 并获取System.MethodAccessException: Attempt by method 'Accessor.SetField0(IRecord`1<Entity>, Int32)' to access IRecord`1<Entity>.get_FieldValues()' failed. 调用生成的 setter 时。

我究竟做错了什么？ 我为此花了一整天，非常沮丧。 任何帮助将不胜感激！

Answer 1

固定的。

1. IRecord<T>接口必须是public ；

2. 删除两行发出的操作码：

private static void EmitGetter(this ILGenerator methodBody, Type fieldValuesType, string fieldName)
{
    methodBody.Emit(OpCodes.Ldarg_0);
    methodBody.Emit(OpCodes.Callvirt, fieldValuesType.FieldValues());
    methodBody.Emit(OpCodes.Ldfld, fieldValuesType.Field(fieldName));
    //methodBody.Emit(OpCodes.Stloc_0); --removed
    //methodBody.Emit(OpCodes.Ldloc_0); --removed
    methodBody.Emit(OpCodes.Ret);
}