Creating dynamic types in VB.NET

runtimeTypes.vb

Public Function Build() As String
 Dim json = String.Empty

 Dim assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(New AssemblyName(_topLevelObjectName), AssemblyBuilderAccess.RunAndSave)
 Dim moduleBuilder = assemblyBuilder.DefineDynamicModule(_topLevelObjectName, String.Format("{0}.dll", _topLevelObjectName))
 Dim typeBuilder = moduleBuilder.DefineType(_topLevelObjectName, TypeAttributes.Class Or TypeAttributes.Public)
 Dim constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public,
                 CallingConventions.Standard,
                 Nothing)
 Dim constructorIL = constructorBuilder.GetILGenerator()
 constructorIL.Emit(OpCodes.Ldarg_0)
 constructorIL.Emit(OpCodes.Call, GetType(Object).GetConstructor(Type.EmptyTypes))
 constructorIL.Emit(OpCodes.Ret)

 For Each constant In Types.Constants
  Dim field = typeBuilder.DefineField(String.Format("_{0}", constant.Name),
           constant,
           FieldAttributes.Private)
  Const getSetAttributes As MethodAttributes = MethodAttributes.Public Or MethodAttributes.SpecialName Or MethodAttributes.HideBySig

  Dim getter = typeBuilder.DefineMethod(String.Format("get_{0}", constant.Name),
             getSetAttributes,
             constant,
             Type.EmptyTypes)
  Dim propertyGetterIL = getter.GetILGenerator()
  propertyGetterIL.Emit(OpCodes.Ldarg_0)
  propertyGetterIL.Emit(OpCodes.Ldfld, field)
  propertyGetterIL.Emit(OpCodes.Ret)

  Dim setter = typeBuilder.DefineMethod(String.Format("set_{0}", constant.Name),
             getSetAttributes,
             Nothing,
             New Type() {constant})
  Dim numberSetIL = setter.GetILGenerator()
  numberSetIL.Emit(OpCodes.Ldarg_0)
  numberSetIL.Emit(OpCodes.Ldarg_1)
  numberSetIL.Emit(OpCodes.Stfld, field)
  numberSetIL.Emit(OpCodes.Ret)

  Dim propertyBuilder = typeBuilder.DefineProperty(constant.Name, PropertyAttributes.HasDefault, constant, Nothing)
  propertyBuilder.SetGetMethod(getter)
  propertyBuilder.SetSetMethod(setter)
 Next
 Dim typeInstance = typeBuilder.CreateType()
 assemblyBuilder.Save(String.Format("{0}.dll", assemblyBuilder.GetName().Name))
 Dim instance = Activator.CreateInstance(typeInstance)
 json = JsonConvert.SerializeObject(instance, Formatting.Indented)
 Return json
End Function