Question

Can I use an anonymous type as a return type in a Function, and then stuff that returned value into an array or collection of some sort whilst also adding an additional field to the new array/collection? excuse my pseudocode…

private var GetRowGroups(string columnName)
{
var groupQuery = from table in _dataSetDataTable.AsEnumerable()
                             group table by new { column1 = table[columnName] }
                                 into groupedTable
                                 select new
                                 {
                                     groupName = groupedTable.Key.column1,
                                     rowSpan = groupedTable.Count()
                                 };
    return groupQuery;

}

private void CreateListofRowGroups()
{
    var RowGroupList = new List<????>();
    RowGroupList.Add(GetRowGroups("col1"));
    RowGroupList.Add(GetRowGroups("col2"));
    RowGroupList.Add(GetRowGroups("col3"));

}

Answer 1

This is a very popular question. In general you cannot return an anonymous type due to the requirement of strong typing. However there are a couple of workarounds.

1. Create a simple type to represent the return value. (See here and here). Make it simple by generating from usage.
2. Create a helper method to cast to the anonymous type using a sample instance for casting.