Terrible Colin Logic

The developer job titles are essentially: Junior, Developer, Senior, Principal, then I guess you have Architect which could be seen as a rank above that. Colin is a Principal. In this blog, I document his struggles with simple Junior-level concepts. Using simple AND and OR logic is a prerequisite to being a developer in the first place.

Let’s say you have 4 possibilities which we will label with the letters A, B, C, D and we have some code that checks a variable is one of these types (or not).

He wanted to write some logic that says “Not A or B”. In the programming language C#, “||” is the logical OR, and “!” is NOT which inverts it (so “true” goes to “false”, “false” goes to “true”). So we can denote “Not A or B” as !(A||B). Here it is as a “Truth Table” of how it should work.

Item is	(A||B) “A Or B”	!(A||B) “Not A or B”
A	true	false
B	true	false
C	false	true
D	false	true

but instead, Colin wrote !A || !B (“Not A Or Not B”).

Item is	!A “Not A”	!B “Not B”	!A || !B “Not A Or Not B”
A	false	true	true
B	true	false	true
C	true	true	true
D	true	true	true

So A returns true because it is not B. B returns true because it’s not A. C returns true because it is not A. D returns true because it is not A. So the statement is always true.

A developer points out that it’s nonsense so he has another go. His new method was

A || !B || C || !D

“A Or Not B Or C or Not D”. It’s getting really confusing now, but also returns true for everything.

Item is	A	!B	C	!D	A || !B || C || !D
A	true	true	false	true	true
B	false	false	false	true	true
C	false	true	true	true	true
D	false	true	false	false	true

I couldn’t believe he has come up with more nonsense and still not tested it. I didn’t want to tell him exactly because he should be able to tell that he has done it wrong if he glances at that logic, so I left a simple comment along the lines of “this won’t work”. 

Later, after I got back from lunch, I saw that I had a missed call. So I send him a message “If you are calling about my comment, just test your method”.

He calls me back and starts explaining the requirement. I said that I don’t really need to know, I just know the method wasn’t what he wanted. I ask him to look at the method again. It took him 30 seconds or so before he spotted it.

Colin: “Why did I type the exclamation mark? I must have copied and pasted it. I’ll correct this line and you can review it”.

Me: “Aren’t you going to test it?”

Colin: “No, this will work this time”

Me: “Well, you thought the last two times would work. I recommend you look at the logic a bit longer if you’re not going to test it”.

He looks at it for 10 seconds.

Colin: “Oh there’s another exclamation mark. I’ll change that too”.

He got it right with a bit of supervision, but I don’t think he had much intention of testing it.