用TypeBuilder自引用类属性

Question

我尝试构建运行时类型生成器，但是我遇到了自引用类型属性的鸡蛋和鸡问题。我正在使用TypeBuilder，基本上我要传递一个属性名称及其类型的列表，然后生成一个类型--只要在创建时知道类型，它就能正常工作。然而，我想要实现这个基本概念

  public class Person
  {
      public string Name { get; set; }
      public Person Child { get; set; }
  }

我几乎被困住了。我如何告诉TypeBuilder我想要一个尚未创建的类型的属性？CLR是怎么做到的？

我的当前代码

public class FieldDescription
{
    public string FieldName { get; set; }
    public Type FieldType { get; set; }
  
}

public static class CustomTypeBuilder
{

    public static Type CompileResultType(List<FieldDescription> fields, string TypeName)
    {
        TypeBuilder tb = GetTypeBuilder(TypeName);
       
        ConstructorBuilder constructor = tb.DefineDefaultConstructor(MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName);

        foreach (var field in fields)
            CreateProperty(tb, field);

        Type objectType = tb.CreateType();
        return objectType;
    }

    private static TypeBuilder GetTypeBuilder(string typeSignature)
    {

        var an = new AssemblyName(typeSignature);
        AssemblyBuilder assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run);
        ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MyModule");
        TypeBuilder tb = moduleBuilder.DefineType(typeSignature,
                TypeAttributes.Public |
                TypeAttributes.Class |
                TypeAttributes.AutoClass |
                TypeAttributes.AnsiClass |
                TypeAttributes.BeforeFieldInit |
                TypeAttributes.AutoLayout,
                null);

        FieldBuilder fieldBuilder = tb.DefineField("_ToStringValue", typeof(string), FieldAttributes.Private);
        return tb;
    }

    private static void CreateProperty(TypeBuilder tb, FieldDescription field)
    {
        string propertyName = field.FieldName;
        Type propertyType = field.FieldType ?? tb;
       

        FieldBuilder fieldBuilder = tb.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);

        PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);

       

        MethodBuilder getPropMthdBldr = tb.DefineMethod("get_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig | MethodAttributes.Virtual, propertyType, Type.EmptyTypes);
      
        ILGenerator getIl = getPropMthdBldr.GetILGenerator();

        getIl.Emit(OpCodes.Ldarg_0);
        getIl.Emit(OpCodes.Ldfld, fieldBuilder);
        getIl.Emit(OpCodes.Ret);

        MethodBuilder setPropMthdBldr =
            tb.DefineMethod("set_" + propertyName,
              MethodAttributes.Public |
              MethodAttributes.SpecialName |
              MethodAttributes.HideBySig | MethodAttributes.Virtual,
              null, new[] { propertyType });

        ILGenerator setIl = setPropMthdBldr.GetILGenerator();
        Label modifyProperty = setIl.DefineLabel();
        Label exitSet = setIl.DefineLabel();

        setIl.MarkLabel(modifyProperty);
        setIl.Emit(OpCodes.Ldarg_0);
        setIl.Emit(OpCodes.Ldarg_1);
        setIl.Emit(OpCodes.Stfld, fieldBuilder);

        setIl.Emit(OpCodes.Nop);
        setIl.MarkLabel(exitSet);
        setIl.Emit(OpCodes.Ret);

        propertyBuilder.SetGetMethod(getPropMthdBldr);
        propertyBuilder.SetSetMethod(setPropMthdBldr);
    }
}

Answer 1

CreateProperty允许通过为field.FieldType设置null的方式传递field.FieldType，在这种情况下，TypeBuilder tb类型将用作属性类型。

所以把null传递给FieldType和everything 应起作用

var compileResultType = CustomTypeBuilder.CompileResultType(new List<FieldDescription>
    {
        new() { FieldName = "Test1", FieldType = typeof(string) },
        new() { FieldName = "Test2", FieldType = null } // property of the type being created
    },
    "TypeToTest");
var instance = Activator.CreateInstance(compileResultType);
var test1PI = compileResultType.GetProperty("Test1");
var test2PI = compileResultType.GetProperty("Test2");
test1PI.SetValue(instance, "test");
test2PI.SetValue(instance, instance);
Console.WriteLine(test1PI.GetValue(instance)); // prints test
Console.WriteLine(test2PI.GetValue(instance)); // prints TypeToTest