"The real question is how to avoid code duplication when performing an identical operation on two different properties of an object."
This is a very good question as this situation arises all the time. I think, one of the best ways to deal with this situation is to use the following pattern.
public class O {
int A;
int B;
}
public doOperationX1() {
doOperationX(something to indicate which property to use);
}
public doOperationX2() {
doOperationX(something to indicate which property to use);
}
private doOperationX(input ) {
// actual work is done here
}
In this pattern, the actual implementation is performed in a private method, which is called by public methods, with some extra information. For example, in this case, it can be doOperationX(A), or doOperationX(B), or something like that.
My Reasoning: In my opinion this pattern is optimal as it achieves two main requirements:
It keeps the public interface descriptive and clear, as it keeps operations separate, and avoids flags etc that you also mentioned in your post. This is good for the client.
From the implementation perspective, it prevents duplication, as it is in one place. This is good for the development.