Question

I need to store a list of int–string key-value pairs with a requirement to preserve the order in which items were added. Once it is initialized, it does not change, i.e. nothing added or removed..

At first I thought of using Dictionary<int,string> and everytime I need to access the items use

foreach(var entry in dict.OrderBy(e=>e.Key)) { } //as Key is `int`

However everytime ordering does not seem to be the best option to use.

Now I’ve come to an idea to have a List<Tuple<int, string>>, as soon as List<T> guarantees the order of items.

So, is there a better option?

Answer 1

Looking at the proposed possibilities:

• Dictionary doesn’t guarantee the order of the items
• SortedDictionary sorts the items, but not in the order you added them (it sorts based on key comparison),
• OrderedDictionary keeps the order, but it’s not generic and would introduce unnecessary casting and boxing.

So I think you should use List<Tuple<int, string>>. It preserves order and it’s good enough for iteration using foreach and indexed access. If you know the size in advance, you could use an array as well, or a read only collection type, as Cuong Le suggested in his answer.