Reflection and Nullable in .Net 2.0

[Joe Bloggs]

Hi,

Can someone please kindly show me how to determine if a type (read value
type) is Nullable.

MSDN has this KB:
How to: Identify a Nullable Type (C# Programming Guide)
http://msdn2.microsoft.com/en-us/library/ms366789.aspx

however, using their code snippet, I couldn't get it to work:

public class MyClass
{
public static void Main()
{
Nullable<intj = new Nullable<int>(2 0);
Type type = j.GetType();
if (type.IsGeneric Type && type.GetGeneric TypeDefinition( ) ==
typeof(Nullable <>))
{
Console.WriteLi ne("j is Nullable");
}
else
Console.WriteLi ne("j is NOT Nullable");

Console.WriteLi ne("Type of j is {0}", j.GetType());
}
}

The Output I got is:

j is NOT Nullable
Type of j is System.Int32

thus, is there no way to determine a nullable or an non-nullable value
types?

Thanks for your help in advanced.

[Barry Kelly]

"Joe Bloggs" <es***@rocketma il.comwrote:

Can someone please kindly show me how to determine if a type (read value
type) is Nullable.

If you have the value in a variable of type object, you cannot. See
below for more details.

MSDN has this KB:
How to: Identify a Nullable Type (C# Programming Guide)
http://msdn2.microsoft.com/en-us/library/ms366789.aspx

The documentation on this page reads:

"Calling GetType on a Nullable type causes a boxing operation to be
performed when the type is implicitly converted to Object. Therefore
GetType always returns a Type object that represents the underlying
type, not the Nullable type."

Thus, the behaviour you're getting is as documented.

Nullable<intj = new Nullable<int>(2 0);
Type type = j.GetType();

Nullable<Tdoesn 't override GetType(), so this method call ends up
boxing j. The way boxing nullable types works on the CLR is that null
values get turned into null references, while non-null inner values get
boxed into the inner type.

So, j, of type Nullable<int(ak a int?), when boxed, is of type int
(i.e. System.Int32).

thus, is there no way to determine a nullable or an non-nullable value
types?

It is impossible to get a boxed nullable value in a variable of type
object. They do not occur. The boxed nullable value is either null or of
the inner type. Casting back to a nullable type performs the appropriate
null check automatically.

-- Barry

--
http://barrkel.blogspot.com/