First, I agree that the whole concept of generics is just to prevent the
problems as everyone has stated.
Yet, I have a good reason for wanting such a cast.
Take for example this generic class:
public static class FixDBNull<ItemType> {
/// <summary>
/// Verifys that the specified data is not DBNULL.
/// If so, it returns the empty value.
/// </summary>
/// <param name="data">The data to verify.</param>
/// <param name="nullValue">The null value to return if data is
DBNULL</param>
/// <returns></returns>
public static ItemType Convert(object data, ItemType nullValue) {
if (data != System.DBNull.Value) {
return (ItemType)data;
}else {
return nullValue;
}
}
}
You use this class/function this way:
... = FixDBNull<string>.Convert(dr["myStringColumn1"], null);
... = FixDBNull<byte[]>.Convert(dr["myByteArrayColumn1"], null);
... = FixDBNull<string>.Convert(dr["myStringColumn2"], "myNullValue");
Note: this will fail:
... = FixDBNull<bool>.Convert(dr["myIntColumn1"], false);
Notice that I have "(ItemType)data" which means I'm attempting to cast
whatever "data" is to whatever ItemType is.
Since I use this stritcly for database manipulations where the value
returned - data - can be an int and it really represents a bool.
(I realize this could start another argument regarding the usage of int vs
bit for boolean types, but for the purposes of this discussion, let's just
assume it's valid).
Since the compiler will cast object to string (or attempt to do so) and
object to int, and object to byte[], and object to other intrinsic types
(except boolean) this generic class/function works quite well for intrinsic
data types except for boolean.
And it's also (for the purposes of this function) desired for an
InvalidCastException to be raised when the cast is invalid; but when you
know the type of data your column will return, the cast should always work.
And since you cannot use the equality (or inequality) operators (=, != ) in
testing the values to two generic parameters there's no way to determine if
the object is a boolean to test a particular value (example: nullValue will
never be equal to true or false).
Yes, perhaps some of this can be overcome with Nullable types, so if any of
you have any suggestions how I can revise my code to allow for nullable
types, I'd like to see it.
Thanks,
Mike
On 8/3/06, Chris Anderson <[EMAIL PROTECTED]> wrote:
bool x = (value != 0);
> -----Original Message-----
> From: Discussion of advanced .NET topics.
> [mailto:[EMAIL PROTECTED] On Behalf Of Mike Andrews
> Sent: 03 August 2006 14:16
> To: [email protected]
> Subject: [ADVANCED-DOTNET] Gripe out the C# compiler...
>
> Guys,
>
> Can anyone tell me any good reason why the C# compiler will
> not allow casting an int to a bool?
>
> example:
>
> bool x = (bool)1;
>
>
> instead of doing something like this:
> bool x = Convert.ToBoolean(1);
> or
> bool x = bool.Parse(1);
>
> Makes it very difficult to write generic methods where I need
> to cast a value to a bool.
>
> Thanks,
> Mike
>
> ===================================
> This list is hosted by DevelopMentor(r) http://www.develop.com
>
> View archives and manage your subscription(s) at
> http://discuss.develop.com
>
>
>
===================================
This list is hosted by DevelopMentor(r) http://www.develop.com
View archives and manage your subscription(s) at
http://discuss.develop.com
===================================
This list is hosted by DevelopMentor® http://www.develop.com
View archives and manage your subscription(s) at http://discuss.develop.com
