unwrap T from Nullable

Question

Wanted a simple but efficient method to get value from Nullable when T is not known at the compile time.

So far have something like this:

public static object UnwrapNullable(object o)
{
    if (o == null)
        return null;

    if (o.GetType().IsGenericType && o.GetType().GetGenericTypeDefinition() == typeof(Nullable<>))
        return ???

    return o;
}

anything can be done here without dipping into dynamic code generation?

used on .NET 2.0

Do you that the object is a Nullable, or do you not even know that much? If you know o is a Nullable, then calling o.GetType() will return T. — dlev, May 12 '11 at 15:48
Agree with dlev - why doesn't this function just take a Nullable? — Tesserex, May 12 '11 at 15:49
Also, why unwrap `Nullable` if you're just going to return `null`!? — user7116, May 12 '11 at 15:55
@Tesserex, ICR: I'm guessing that this is done via reflections, hence he gets `object` back. — Merlyn Morgan-Graham, May 12 '11 at 16:10

score 7 · Accepted Answer · answered May 12 '11 at 15:53

o can never refer to an instance of Nullable<T>. If you box a nullable value type value, you either end up with a boxed value of the non-nullable underlying type, or a null reference.

In other words, o.GetType() can never return Nullable<T> for any value of o - regardless of the type of o. For example:

Nullable<int> x = 10;
Console.WriteLine(x.GetType()); // System.Int32

Here we end up boxing the value of x because GetType() is declared on object and not overridden in Nullable<T> (because it's non-virtual). It's a little bit of an oddity.

hmmm yes I guess I didn't think that one through. – Ilia G May 12 '11 at 16:15 — Ilia G, May 12 '11 at 16:15

score 0 · Answer 2 · answered May 12 '11 at 15:54

0

It does not makes sense.

If you have code:

int? x = null; //int? == Nullable<int>
if ( null == x ) { Console.WriteLine("x is null"); }
else { Console.WriteLine( "x is " + x.ToString() ); }

The result will be "x is null" printed in console.

answered May 12 '11 at 15:54

TcKs

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unwrap T from Nullable

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