Question

If I have a using block surrounding a try catch statement what will happen to the object inside that using statement should the catch fire an exception? Consider the following code:

using (IDatabaseConnectivityObject databaseConnectivityObject = new DbProviderFactoryConnectionBasicResponse())
{
    try
    {
        Foo();
    }
    catch (ArgumentNullException e)
    {
        throw;
    }
}

If we assume Foo() fails and the exception is fired and effectively breaks the program will databaseConnectivityObject be disposed? The reason this is important is that the object has a database connection associated with it.

Answer 1

You can think of using as a short-hand for try-finally. Hence your code is equivalent to:

IDatabaseConnectivityObject databaseConnectivityObject = new DbProviderFactoryConnectionBasicResponse();
try
{
    try
    {
        Foo();
    }
    catch(ArgumentNullException e)
    {
        throw;
    }
}
finally
{
  if(databaseConnectivityObject != null)//this test is often optimised away
    databaseConnectivityObject.Dispose()
}

Looked at this way, you can see that the Dispose() will indeed be called if the exception throws, because the try-finally is outside of the try-catch.

This is precisely why we use using.