When someone is asking about, for example, how to add a feature, or change behavior to/of some program for which you know it is not possible, is it acceptable to post a "this is not possible" answer?
I know this is not an answer in itself, but then there is a dilemma:
Leaving the question without answer (in this case, the user can wonder if simply his question had no success, and he would eventually start a bounty for something which can't be answered).
Answering "there is no solution", and explaining why (which would provide information to the user, but at the price of discouraging further answers, and of course the risk of simply being wrong).
What would you recommend to do in such situation?
Edit: Bonus question: When there is such an answer, what about the voting behavior? Should such answer be upvoted if you agree that indeed, there is no solution? In the end, this is not giving any solution, so it looks strange to vote for it.