Most efficient way to check three objects for not being null OR only two of them can be null

Question

I am struggling with a problem of validating three objects (A, B, C)

These are my conditions

• none of then can be null
• at most one of then can be not null

I want to resolve it without many if expression and creating monstrous code.

So

  A  B  C
A 1  0  0
B 0  1  0
C 0  0  1

as it show I need to achieve something like this pseudo table before only one of them can be true and all the other are false

Final

what expression can provide such validation?

Answer 1

Create a helper method to do it (with tests), then at that point, have the code as messy or as clean as you wish in order to achieve your targets.

This is a fairly simple implementation; guarantees exactly 3 checks every time.

public static bool OnlyOneNotNull(object object1, object object2, object object3)
{
    if (object1 != null)
        return object2 == null && object3 == null;

    if (object2 != null)
        return object3 == null;

    return object3 != null;
}

Usage is simply:

if (OnlyOneNotNull(A, B, C))
{
    //do something
}