No type inference with DataRowCollection

Question

I have a project that stores some data from SQL in a DataTable and then maps each DataRow to a custom class instance.

When I loop over the Rows property (which is of type DataRowCollection), there's no type inference.

So this doesn't work:

var dt = new DataTable();
foreach(var row in dt.Rows)
{
    int id = Int32.Parse(row.ItemArray[0].ToString());
    // doesn't compile
}

But this does:

var dt = new DataTable();
foreach(DataRow row in dt.Rows)
{
    int id = Int32.Parse(row.ItemArray[0].ToString());
}

Why can't the compiler figure out of what type the row is? Could the var keyword stand for something else in the case of enumerating over a DataRowCollection? Is there something else, besides data rows, that could be enumerated over in a DataRowCollection?

Is that why you would need to be explicit?

Answer 1

Because DataRowCollection implements IEnumerable(via InternalDataCollectionBase) but not the generic, typed IEnumerable<T>. The class is simply too old.

By specifying the type in the foreach you're casting it implicitely.