Question

Do the keys of a Dictionary need to be comparable with equality?

For example

Class mytype
{
    public bool equals(mytype other)
    {
        return ...;
    }
}

In my case they won’t be equal unless they are the same instance.

If I need to implement equality should I have a large numeric value that increments with every new instance of mytype created?

Answer 1

If your classes are only equal if they are same instance, then you don’t need to do anything to use them in a Dictionary. Classes (reference types) are considered equal if and only if the refer to the same object.

From the documentation of GetHashCode

For derived classes of Object, the GetHashCode method can delegate to the Object.GetHashCode implementation, if and only if that derived class defines value equality to be reference equality and the type is not a value type.

Which seems to be true in your case. As a rule of thumb, if you override Equal you need to override GetHashCode as well but this is not necessary in your case as the default is what you are looking for.