On 1/23/2018 at 3:27 AM, Nypyren said:

Ah, so it does.  I'm thinking of a different case, I guess.  There is at least one situation which looks similar to your example which compiles but discards the modification instead of producing a compile error.  Can't remember exactly what it is now, though.

Little off-topic, but it throws it away in case Address would be a function rather than a property. I.e. Person.GetAddress().City will compile, but throw away the result.

On 1/23/2018 at 1:23 AM, frob said:

Then why not ask them directly?

This precisely. This can make you start a discussion much more easily and can get you to learn a lot more about the programmer. As has been said before, these are all 'spot-the-bug'-kind of questions where you either catch it or are like 'aaah' (which doesn't tell you much; he either didn't know or he knows what's going on, but just happened to oversee it). Interviews can be stressful so it becomes easier to overlook such things. Starting an actual conversation rather than turning it into an exam will make candidates feel more at ease and get the interview to line up more with their normal workflow. 

I get how you're interested in the interviewee's knowledge of C#, but I suggest you leave out exam questions to exams as much as possible and start conversations instead, such as by asking 'what is the difference between a reference and a value type in C#?'. For this particular example, you could, if you're really keen on it, ask the code-example question while or after discussing the topic. I know that in normal cases of problem solving you get no such hint of topic, but in this case it shows the candidate at least requires some additional knowledge to answer the question.