Question

What does this error mean in this context?

if (value == null)
    return "";

if (value is Nullable && ((INullable)value).IsNull) //error on this line
    return "";

if (value is DateTime)
{
    if (((DateTime)value).TimeOfDay.TotalSeconds == 0)
        return ((DateTime)value).ToString ("yyyy-MM-dd");
    return ((DateTime)value).ToString ("yyyy-MM-dd HH:mm:ss");
}

I searched but didn’t get any information on this error. I am trying this on Mono (2.10.8.1). This is a project actually meant for Windows, but when I tried to compile it in Monodevelop, I got this error.

Answer 1

The problem is here:

if (value is Nullable

It thinks you’re talking about the static class System.Nullable rather than the System.Nullable<T> struct.

Perhaps you meant:

if (value is INullable ...)

?

Note that if value is of compile-time type object, then it will never be a Nullable<T>, as boxing a null value would give a null reference, and boxing a non-null value would give a boxed value of the underlying type.

If you think there’s still something else which you need to achieve, please specify what you’re trying to do.