How can I create new object based on another one?

Question

I have some not useful object with, let's say, 30 properties. Half of them are useful for me, so I want to create new useful object with only properties I need so the rest doesn't take space in object visualizers. I don't want to define new class and type them down. I want something like

var list = new List<SomeType> { usefulProp1, usefulProp2, ... };
var usefulObject = new NewItem(notUsefulObject, list);

where SomeType is not string (list doesn't contain property names).

Answer 1

var list = new List<Expression<Func<object>>> { () => notUsefulObject.usefulProp1, () => notUsefulObject.usefulProp2... };
var nm = new AssemblyName("MyDynamicAssembly");
TypeBuilder tb = Thread.GetDomain().DefineDynamicAssembly(nm, AssemblyBuilderAccess.RunAndSave).DefineDynamicModule(nm.Name, nm.Name + ".dll").DefineType("NewItem", TypeAttributes.Public);
const MethodAttributes GetSetAttr = MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig;
foreach (Expression b in list.Select(x => x.Body))
{
    MemberInfo mi = ((MemberExpression)b).Member;
    Type t = b.Type;
    FieldBuilder fb = tb.DefineField(mi.Name.ToLower(), t, FieldAttributes.Private);
    PropertyBuilder pb = tb.DefineProperty(mi.Name, PropertyAttributes.HasDefault, t, null);
    MethodBuilder getBld = tb.DefineMethod("get_" + mi.Name, GetSetAttr, t, Type.EmptyTypes);
    ILGenerator getGen = getBld.GetILGenerator();
    getGen.Emit(OpCodes.Ldarg_0);
    getGen.Emit(OpCodes.Ldfld, fb);
    getGen.Emit(OpCodes.Ret);
    MethodBuilder setBld = tb.DefineMethod("set_" + mi.Name, GetSetAttr, null, new[] { t });
    ILGenerator setGen = setBld.GetILGenerator();
    setGen.Emit(OpCodes.Ldarg_0);
    setGen.Emit(OpCodes.Ldarg_1);
    setGen.Emit(OpCodes.Stfld, fb);
    setGen.Emit(OpCodes.Ret);
    pb.SetGetMethod(getBld);
    pb.SetSetMethod(setBld);
}
object usefulObject = Activator.CreateInstance(tb.CreateType());