I want "(int)null" to return me 0.

Question

How can i get 0 as integer value from (int)null.

EDIT 1: I want to create a function that will return me default values for null representation in their respective datatypes.

EDIT 2: How can i work in this scenario for using default.

(int)Value

Where Value can be null or any integer value. I dont know datatype of value at run time. But i will assure that Value should either contain null or Integer value only.

Answer 1

You can't cast a null to an int, as an int is a value type. You can cast it to an int? though.

What is it you want to achieve?

Answer 2

You can use the Nullable structure

int value = new Nullable<int>().GetValueOrDefault();

You can also use the default keyword

int value = default(int);

Following 2nd edit:

You need a function that receive any type of parameter, so object will be used. Your function is similar to the Field<T> extension method on a DataRow

public static T GetValue<T>(object value)
{
    if (value == null || value == DBNull.Value)
        return default(T);
    else
        return (T)value;
}

Using that function, if you want an int (and you expect value to be an int) you call it like:

int result = GetValue<int>(dataRow["Somefield"]);

Answer 3

You can use the default keyword to get the default value of any data type:

int x = default(int);        //  == 0
string y = default(string);  //  == null
// etc.

This works with generic parameters as well:

Bar<T> Foo<T>() {
    return new Bar<T>(default(T));
}

---

In case you have a variable of type object that may contain null or a value of type int, you can use nullable types and the ?? operator to convert it safely to an integer:

int a = 42;
object z = a;
int b = (int?)z ?? 0;        //  == 42
int c = (int?)null ?? 0;     //  == 0

Answer 4

A generic method that returns a cast instance of an object or the default value could be implemented as follows:

static T Cast<T>(object value) {
    if (value is T)
        return (T)value;
    else
        return default(T);
}

This way, using a valid value will yield the value itself:

int value = Cast<int>(4); //value = 4

and a null value will get the default:

int value = Cast<int>(null); //value = 0

Notice that since the method takes object as an argument, this will cause boxing when used with struct objects (like int).

Answer 5

A method of a generic class that returns nothing works:

 Class GetNull(Of T)
      Public Shared Function Value() As T
           Return Nothing
      End Function
 End Class



 Debug.Print(GetNull(Of Integer).Value())

Answer 6

Check out this post for a mostly complete method for writing an extension to do just this. My scenario is pulling data from a NameValueCollection.

http://hunterconcepts.com/blog/Extensions_HttpRequestFormQueryString/