OrderBy and List vs. IOrderedEnumerable
c#, linq
Solution
Why not just sort the list in place using the `Sort()` instance method; then you can add items to it later if you like:
List<string> items = GetSomeItems();
items.Sort();
Or, use an ordered collection like a binary search tree. `SortedSet<T>` might fit the bill, depending on your needs.
The solution suggested by the others:
items = items.OrderBy(item => item).ToList();
... creates another list with the original items in a new order. This is only useful if you need to preserve the original ordering for some other purpose; it's rather more wasteful of memory than sorting the list in place.
As far as understanding the error, it's simple: `List<T>` isn't a subtype of `IOrderedEnumerable<T>`, so there's no implicit reference conversion between the two. The explicit cast that the compiler suggests will satisfy the compiler, but it will fail at run time because the object returned by `OrderBy<T>` does not inherit from `List<T>`.
EDIT
An example of `List<T>.Sort(Comparison<T>)`, assuming the type `MyType` has a `Key` property of some type type T where `T : IComparable<T>`:
List<MyType> items = GetSomeItems();
items.Sort((a, b) => a.Key.CompareTo(b.Key));
Problem
I ran across an unexpected problem with the following code. ``` List<string> items = new List<string>(); items = items.OrderBy(item => item); ``` This code generates the error: Cannot implicitly convert type 'System.Linq.IOrderedEnumerable' to 'System.Collections.Generic.List'. An explicit conversion exists (are you missing a cast?) It appears I can change `items` to be of type `IEnumerable<string>` and the error goes away. But I need to be able to add items to the list, which `IEnumerable` doesn't support. Can someone help me understand this error, and what the easiest fix is? Is it safe to simply cast the result?