How to add a constraint of Nullable Types to a generics method

[Joe Bloggs]

Hi,

compiling the following code:

public class App
{
static void Main()
{
int? x = 5;
bool? i = null;
Console.WriteLi ne(GetType(x).F ullName);
Console.WriteLi ne(" x={0}", GetSafeValue(x) );
Console.WriteLi ne(" i={0}", GetSafeValue(i) );
Console.ReadLin e();
}
public static object GetSafeValue<T, N>(T value) where T:struct
{

if (!IsNullableVal ueType(GetType( value)))
{
Console.WriteLi ne(" {0} is not a Nullable type", value.GetType() );
return value;
}
object nullableValue = value;

return nullableValue ??
GetDefaultDataT ypeValue((GetTy pe(value)).GetG enericArguments ()[0]);

}
}

I get the error message
"The type 'int?' must be a non-nullable value type in order to use it
as parameter 'T' in the generic type or method
'App.GetSafeVal ue<T>(T)'"

Obviously, I have set the constraint to only accept value types.

Now, how do I modify the constraint so that I can accept either value
types or Nullable types?

Thanks in advance.

[Nicholas Paldino [.NET/C# MVP]]

Joe,

Why not just get the Value on the nullable to begin with? It will
return a default value if it is "null" (meaning, it is flagged as null, it
isn't actually null).

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

"Joe Bloggs" <es***@rocketma il.comwrote in message
news:11******** **************@ 75g2000cwc.goog legroups.com...

Hi,

compiling the following code:

public class App
{
static void Main()
{
int? x = 5;
bool? i = null;
Console.WriteLi ne(GetType(x).F ullName);
Console.WriteLi ne(" x={0}", GetSafeValue(x) );
Console.WriteLi ne(" i={0}", GetSafeValue(i) );
Console.ReadLin e();
}
public static object GetSafeValue<T, N>(T value) where T:struct
{

if (!IsNullableVal ueType(GetType( value)))
{
Console.WriteLi ne(" {0} is not a Nullable type", value.GetType() );
return value;
}
object nullableValue = value;

return nullableValue ??
GetDefaultDataT ypeValue((GetTy pe(value)).GetG enericArguments ()[0]);

}
}

I get the error message
"The type 'int?' must be a non-nullable value type in order to use it
as parameter 'T' in the generic type or method
'App.GetSafeVal ue<T>(T)'"

Obviously, I have set the constraint to only accept value types.

Now, how do I modify the constraint so that I can accept either value
types or Nullable types?

Thanks in advance.

[Barry Kelly]

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

public static object GetSafeValue<T, N>(T value) where T:struct

Yes, struct excludes nullable types.

Obviously, I have set the constraint to only accept value types.

Now, how do I modify the constraint so that I can accept either value
types or Nullable types?

You can't do it statically. You'll have to do it at runtime.

-- Barry

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