Question

Can you please explain what is happening here?

using(DataSet ds = GetDataSet()) // will this get disposed? if yes (when?)
{
    using(DataTable dt = ds.Tables[0]) /* in this line is ds available for dt? i found some issue with this kind of statement. dt gets null after this line */
    {
          // i know that ds is available here.
          //some code
    }
}

Answer 1

using(DataSet ds = GetDataSet()){

  using(DataTable dt = ds.Tables[0])
  // dt will be NULL if there are no tables in ds
  {
    // both dt & ds will be available here

  }// dt will get disposed

}// ds will be disposed at this point...

The equivalent code for this is:

try{
 DataSet ds = GetDataSet();
 try{
  DataTable dt = ds.Tables[0];
  // dt will not be null if there are any tables in ds
  // Both ds & dt available here...
 }
 finally{
  dt.Dispose();
 }
}
finally{
 ds.Dispose();
}