c# modifying structs in a List

Question

Short question: How can I modify individual items in a List? (or more precisely, members of a struct stored in a List?)

Full e

Answer 1

The foreach loop doesn't work because sInf is a copy of the struct inside items. Changing sInf will not change the "actual" struct in the list.

Clear works because you aren't changing sInf, you are changing the list inside sInf, and Ilist will always be a reference type.

The same thing happens when you use the indexing operator on IList - it returns a copy instead of the actual struct. If the compiler did allow catSlots[s].subItems = sortedSubTemp;, you'll be modifying the subItems of the copy, not the actual struct. Now you see why the compiler says the return value is not a variable - the copy cannot be referenced again.

There is a rather simple fix - operate on the copy, and then overwrite the original struct with your copy.

for (int s = 0; s < gAllCats[c].items.Count; s++)
{
            var sortedSubItems =
                            from itemInfo iInf in gAllCats[c].items[s].subItems
                            orderby iInf.subNum ascending
                            select iInf;
            IList sortedSubTemp = new List();
            foreach (itemInfo iInf in sortedSubItems)
            {
                            sortedSubTemp.Add(iInf);
            }
            var temp = catSlots[s];
            temp.subItems = sortedSubTemp;
            catSlots[s] = temp;
}

Yes, this results in two copy operations, but that's the price you pay for value semantics.