What would you recommend for class that needs to keep a list of unique integers?
I'm going to want to Add() integers to the collection and also check for existence e.g. Contains().
Would be nice to also get them in a list as a string for display, ie. "1, 5, 10, 21".
If you can't use .NET 3.5, then you can't use HashSet. If that's the case, it's easy to roll your own based on the Dictionary structure.
public class Set<T> {
private class Unit { ... no behavior }
private Dictionary<T, Unit> d;
....
}
Unit is intended to be a type with exactly one value. It doesn't matter what you map elements to, just use the keys to know what's in your set. The operations you asked for in the question are straightforward to implement.
you could inherit a class from KeyedCollection. This way your key can be the value itself, you can override the ToString so that you get your desired output. This could give you the behaviour you want/need.
Note, this answer was for the framework 2.0 part of the Q
In my testing, I have found that a Dictionary with a dummy value is faster than a HashSet, when dealing with very large sets of data (100,000+ in my case). I expect this is because the Dictionary allows you to set an initial capacity, but I don't really know. In the case you're describing, I would probably use the Dictionary if I was expecting a very large set of numbers, and then (or as I was adding to the Dictionary, depending on the intent) iterate over it using a string builder, to create the output string.