Can a Generic Method handle both Reference and Nullable Value types?
- by Adam Lassek
I have a series of Extension methods to help with null-checking on IDataRecord objects, which I'm currently implementing like this:
public static int? GetNullableInt32(this IDataRecord dr, int ordinal)
{
int? nullInt = null;
return dr.IsDBNull(ordinal) ? nullInt : dr.GetInt32(ordinal);
}
public static int? GetNullableInt32(this IDataRecord dr, string fieldname)
{
int ordinal = dr.GetOrdinal(fieldname);
return dr.GetNullableInt32(ordinal);
}
and so on, for each type I need to deal with.
I'd like to reimplement these as a generic method, partly to reduce redundancy and partly to learn how to write generic methods in general.
I've written this:
public static Nullable<T> GetNullable<T>(this IDataRecord dr, int ordinal)
{
Nullable<T> nullValue = null;
return dr.IsDBNull(ordinal) ? nullValue : (Nullable<T>) dr.GetValue(ordinal);
}
which works as long as T is a value type, but if T is a reference type it won't.
This method would need to return either a Nullable type if T is a value type, and default(T) otherwise. How would I implement this behavior?
