Question

Lets say I have a class

Public Class Person
Public Name As String
Public Rank As String
End Class

And then I have a dictionary which uses these classes as the Key. I have two Person objects, each with the same string value in Name and Rank, but I find that they are not treated as the same key. Can the dictionary not be used this way?

Answer 1

The dictionary does not know how to compare your user-made classes by default. It does not simply compare all fields within the class. As noted in the remarks section for Dictionary<TKey,TValue>:

If type TKey implements the System.IEquatable generic interface, the default equality comparer uses that implementation.

Your person class must implement the IEquatable<T> interface, consisting of an Equals(Person) method, which will return true if the two instances should be treated as equal. Additionally, as noted in remarks for IEquatable<T>:

If you implement IEquatable, you should also override the base class implementations of Object.Equals(Object) and GetHashCode so that their behavior is consistent with that of the IEquatable<T>.Equals method.