Not the GP, but I focus on tradeoffs and roads not taken. Get them to talk about a project they've worked on, and then ask about alternative design decisions around some interesting feature and see what they say.
Example: I developed a little state-machine framework for managing complexity in a large, legacy code-base. It allowed me to refactor a lot of ad hoc distributed logic into the transition table and clean up a lot of weird corner cases that made the code fragile and difficult to change.
Questions might include: "Why did you write your own rather than use an existing state machine framework like the one in boost?" (for C++ frameworks there's pretty much always one in boost, so even if you don't know anything about the area you can throw this in for fun and see what they say). Also: "Why a state machine rather than some other approach to refactoring?" And so on. This process gets at taste and good judgement, it gives you a sense of how tolerant of alternatives they are, and so on.
Additional edit: one of the things I look for in answers is people who say, "Yeah, that particular decision might have been a mistake... I always wondered what would have happened if instead I had..." Good developers are able to admit that not everything they do is perfect, and are willing to give alternative views a bit of credence.
Example: I developed a little state-machine framework for managing complexity in a large, legacy code-base. It allowed me to refactor a lot of ad hoc distributed logic into the transition table and clean up a lot of weird corner cases that made the code fragile and difficult to change.
Questions might include: "Why did you write your own rather than use an existing state machine framework like the one in boost?" (for C++ frameworks there's pretty much always one in boost, so even if you don't know anything about the area you can throw this in for fun and see what they say). Also: "Why a state machine rather than some other approach to refactoring?" And so on. This process gets at taste and good judgement, it gives you a sense of how tolerant of alternatives they are, and so on.
Additional edit: one of the things I look for in answers is people who say, "Yeah, that particular decision might have been a mistake... I always wondered what would have happened if instead I had..." Good developers are able to admit that not everything they do is perfect, and are willing to give alternative views a bit of credence.