Question

I was wondering if there was a built in type in C# that was like ‘Dictionary’ but where both TKey and TValue had to be unique.

For example::

d.Add(1, "1");
d.Add(2, "1"); // This would not be OK because "1" has already been used as a value.

I know this is kind of exotic, but it seems that since there are about a billion collection types in the BCL it might exist. Any ideas?

Answer 1

How about having Dictionary and HashSet/secondary reverse Dictionary – it will solve the issue and will perform better than checks on single Dictionary.

Something like this, wrapped as class:

HashSet<string> secondary = new HashSet<string>(/*StringComparer.InvariantCultureIgnoreCase*/);
Dictionary<int, string>dictionary = new Dictionary<int, string>();
object syncer = new object();

public override void Add(int key, string value)
{
  lock(syncer)
  {
    if(dictionary.ContainsKey(key))
    {
      throw new Exception("Key already exists");
    }

    if(secondary.Add(value)
    {
      throw new Exception("Value already exists");
    }
    dictionary.Add(key, value);
  }
}