C#

using System.Collections.Generic;

static class Program {
	static void Main() {
	}
}

public class ReportBandEntity { public int objcode, foo,bar; };

public class ReportBand {

	public List<ReportBandEntity> EntityList;

	// ... EntityList initialization code skipped

	public struct Group {
		public ReportBandEntity Header, Footer;
	}

	public List<Group> GroupList;

	public void GetGroupList() {

		GroupList = new List<Group>();

		foreach (ReportBandEntity e in EntityList)
			if (e.objcode == 1) {
				Group g = new Group();
				g.Header = e;
				GroupList.Add(g);
			}

		int i = 0;
		foreach (ReportBandEntity e in EntityList)
			if (e.objcode == 2) {
				//Error	2	Cannot modify the return value of 
				// 'System.Collections.Generic.List<mynsp.ReportBand.Group>.
				// this[int]' because it is not a variable	

				GroupList[i++].Footer = e;

				// this does not cause error but does not assign value to
				// GroupList[i++].Footer !
				//Group x = GroupList[i++];
				//x.Footer = e;
			}
	}
}