The using keyword works on objects that implement IDisposable interface (an interface with one member, the Dispose() method).
So a code like this:
using (SqlConnection conn = new SqlConnection("connection_string"))
{
// use conn...
}
Is actually transformed into:
SqlConnection conn = null;
try
{
conn = new SqlConnection("connection_string");
}
finally
{
if (conn!=null)
conn.Dispose();
}
The using keyword allows more elegant writing, nothing more actually.
The additional feature I would like to see is that in case of exception, a method in the implementor of IDisposable will be called, meaning the code should(?) be transformed into something like this:
SqlConnection conn = null;
try
{
conn = new SqlConnection("connection_string");
}
catch(Exception err) // *
{
HandleException(err);
}
finally
{
if (conn!=null)
conn.Dispose();
}
Of course, I would have to implement HandleException(Exception e) method as part of implementing IDisposable interface.
Why is this good for ??
Well, think about creating a transaction scope interface:
interface ITransactionScope : IDisposable
{
void Commit();
void Rollback();
// ....
}
In this scenario, it would be great that if no exceptions were thrown, the transaction should Commit() by default,
but if any exception was thrown and not handled - do Rollback().
using (ITransactionScope trans = DbServices.StartTransactionScope())
{
// delete 1
} // should do Commit()
using (ITransactionScope trans = DbServices.StartTransactionScope())
{
// delete 1
throw new ArgumentException("just to make the point clear");
} // should do Rollback()
HandleException(Exception e) will allow me to set a flag for Rollback on Dispose or to Rollback immediately; This can be quite handy.
Today I Rollback at the Dispose(if the transaction state is "uncommitted") and I force my programmers to call Commit() method directly.
* I know that catching Exception is a bad practice by default, but in those scenarios I would rather ask the "is\as" question(s) and handle my exception than wrapping using with try-catch blocks. After all, using should allow elegant code...
What do you think ?
update:
I've posted a ladybug at Microsoft Product Feedback, you can check it out (and vote!!!) here:
http://lab.msdn.microsoft.com/ProductFeedback/viewfeedback.aspx?feedbackid=f3c7e216-8790-4937-acc0-502848232a9d