Question

I have an object that I want to use to look up other objects. I will be using a Dictionary<TKey, TValue>().

The key object has two strings that uniquely identify it, say KeyObj.Str1 and KeyObj.Str2.

What do you recommend that I use as the key for the dictionary?

1: The concatenation of the strings.

Dictionary<String, TValue>(); Key = KeyObj.Str1:KeyObj.Str2; ('somestring:anotherstring') 

2: A unique integer for each object to identify it?

Dictionary<int, TValue>(); KeyObj.ID = _nextID++; Key = KeyObj.ID; 

3: A reference to the object.

Dictionary<KeyObj, TValue>(); Key = KeyObj; 

Option 3 would be the easiest, but it seems like it would be inefficient to index a dictionary based on reference values.

If the key object contained a single unique string, the obvious choice would be use that, but having two strings that are only unique in combination makes it more difficult.

Answer 1

Concatenated strings should work best.

IF you know that their combination is unique, then that is what you should choose — remember that Hash code is usually unique, but not always.