Collection that allows only unique items in .NET?

Question

Is there a collection in C# that will not let you add duplicate items to it? For example, with the silly class of

public class Customer {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Address { get; set; }

    public override int GetHashCode() {
        return (FirstName + LastName + Address).GetHashCode();
    }

    public override bool Equals(object obj) {
        Customer C = obj as Customer;
        return C != null && String.Equals(this.FirstName, C.FirstName) && String.Equals(this.LastName, C.LastName) && String.Equals(this.Address, C.Address);
    }
}

The following code will (obviously) throw an exception:

Customer Adam = new Customer { Address = "A", FirstName = "Adam", LastName = "" };
Customer AdamDup = new Customer { Address = "A", FirstName = "Adam", LastName = "" };

Dictionary<Customer, bool> CustomerHash = new Dictionary<Customer, bool>();
CustomerHash.Add(Adam, true);
CustomerHash.Add(AdamDup, true);

But is there a class that will similarly guarantee uniqueness, but without KeyValuePairs? I thought HashSet<T> would do that, but having read the docs it seems that class is just a set implementation (go figure).

Answer 1

HashSet<T> is what you're looking for. From MSDN (emphasis added):

The HashSet<T> class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.

Note that the HashSet<T>.Add(T item) method returns a bool -- true if the item was added to the collection; false if the item was already present.