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 explanation: First, the `struct` definitions used below: ``` public struct itemInfo { ...(Strings, Chars, boring)... public String nameStr; ...(you get the idea, nothing fancy)... public String subNum; //BTW this is the element I'm trying to sort on } public struct slotInfo { public Char catID; public String sortName; public Bitmap mainIcon; public IList subItems; } public struct catInfo { public Char catID; public String catDesc; public IList items; public int numItems; } catInfo[] gAllCats = new catInfo[31]; ``` `gAllCats` is populated on load, and so on down the line as the program runs. The issue arises when I want to sort the `itemInfo` objects in the `subItems` array. I'm using LINQ to do this (because there doesn't seem to be any other reasonable way to sort lists of a non-builtin type). So here's what I have: ``` foreach (slotIn…

Accepted Answer

Looking at the for-loop approach, the reason (and solution) for this is given in the documentation for the compilation error:

An attempt was made to modify a value type that is produced as the result of an intermediate expression but is not stored in a variable. This error can occur when you attempt to directly modify a struct in a generic collection.

To modify the struct, first assign it to a local variable, modify the variable, then assign the variable back to the item in the collection.

So, in your for-loop, change the following lines:

```
catSlots[s].subItems.Clear();
catSlots[s].subItems = sortedSubTemp;   // ERROR: see below
```

...into:

```
slotInfo tempSlot = gAllCats[0].items[s];
tempSlot.subItems  = sortedSubTemp;
gAllCats[0].items[s] = tempSlot;
```

I removed the call to the `Clear` method, since I don't think it adds anything.

c# modifying structs in a List<T>

Solution

Problem