Is it possible to clone a ValueType?

Question

Is it possible to clone an object, when it's known to be a boxed ValueType, without writing type specific clone code?

Some code for reference

List<ValueType> values = new List<ValueType> {3, DateTime.Now, 23.4M};
DuplicateLastItem(values);

The partical issue I have is with a value stack based virtual instruction machine. (And Im too lazy to write typeof(int) typeof(DateTime)....)

update I think I confused myself (and a few other people). The working solution I have is;

List<ValueType> values = new List<ValueType> { 3, DateTime.Now, 23.4M }; 

// Clone
values.Add(values[values.Count() - 1]);

// Overwrite original
values[2] = 'p';

foreach (ValueType val in values)
   Console.WriteLine(val.ToString());

Answer 1

I don't know, if I have totally misunderstood the question.
Are you trying to do this?

public static void Main()
{
    List<ValueType> values = new List<ValueType> {3, DateTime.Now, 23.4M};
    DuplicateLastItem(values);

    Console.WriteLine(values[2]);
    Console.WriteLine(values[3]);
    values[3] = 20;
    Console.WriteLine(values[2]);
    Console.WriteLine(values[3]);
}

static void DuplicateLastItem(List<ValueType> values2)
{
    values2.Add(values2[values2.Count - 1]);
}

Answer 2

Every assignment of a valuetype is by definition a clone.

Edit:

When boxing a valuetype a copy of your valuetype will be contained in an instance of a ReferenceType.

Depending of the Cloning method, I don't foresee any differences.

Answer 3

You can use a hack using Convert.ChangeType:

object x = 1;
var type = x.GetType();
var clone = Convert.ChangeType(x, type);

// Make sure it works
Assert.AreNotSame(x, clone);

The result is copy of the value boxed in new object.

Answer 4

Why do you need cloning code anyway? Value types should usually be immutable anyway and this isn’t changed by boxing. Therefore, a well-designed value type has no requirement for cloning.

Answer 5

    private static T CloneUnboxed<T>(object o) where T : struct
    {
        return (T)o;
    }

    private static object CloneBoxed<T>(object o) where T : struct
    {
        return (object)(T)o;
    }

Although I do question the need for either, given that a value type ought to be immutable.

Answer 6

If you were to cast the object to ValueType, would that not cause a clone to be made? This could then be reboxed:

int i = 3;
object b = i; // box it
ValueType c = (ValueType) b; // unbox it
object d = c; // box it, effectively creating a clone

So, I think I would say an effective clone methodology would be:

object clone = (ValueType) boxed;