looking for regex engines comparison and benchmark was closed as "not a real question". The user was told stackexchange does not have a place for technology comparisons. This seems odd for a few reasons:

  1. The question is answerable. The user did not ask for opinions. They asked for feature comparisons and benchmarks. Without doing a lot of research, I've confirmed such things exist. Wikipedia offers a grid of feature comparisons and Heng Li offers benchmarks on sourceforge. I'm not claiming they're perfect resources, but they certainly suggest the question can be answered.
  2. The benchmark portion of the question was already asked on stackoverflow. Granted, it isn't rich with responses, but the fact it exists seems likely to confuse the user. This was the user's first question. As well as closing, someone took the time to downvote them. Classy.
  3. The user was directed to the FAQ for clarification. As far as I can tell, the FAQ doesn't mention anything about technology comparisons being out-of-bounds. The FAQ's core concepts seem to be that your post must be a question and it must be answerable. If I were the user, I would feel I met the FAQ's criteria.
  4. Stackexchange is full of technology comparisons. From P.SE: Python and ruby frameworks equivalent to codeignter (misspelling left intact) , What one should look for when choosing a cross-platform C++ GUI library?, Current C++ IDE options:, Selecting the (right?) technology and environment, etc.

I'm not suggesting this is an amazing question or that it belongs on P.SE. I'll leave that for others to decide. I just assume that our main goal is to be helpful. If I were the user asking the question, I wouldn't feel helped. I would feel like I'd been slapped on the wrist and excluded.

  • Technology X vs Technology Y questions are prohibited in the FAQ see the third point. Although it could be argued that this isn't asking that.
    – Matt Ellen
    Jul 14, 2011 at 17:04
  • 3
    @Matt Ellen - I understand the X vs. Y prohibition when it's Haskell vs. Erlang or Windows vs. Mac, but I really hope we're not suggesting we can't talk about algorithm implementation time and space requirements. Jul 14, 2011 at 17:41
  • 1
    that's a very good point.
    – Matt Ellen
    Jul 14, 2011 at 17:43

3 Answers 3


If you look at the comments on the question, there were several exchanges with the user on how he could improve his question to be on-topic, including a few prompts for more information and links to helpful resources. He opted not to reply or improve his question after asking twice if there was a place he could ask for comparisons of RegEx engines.

I think you might be reading too much into the question: algorithm implementation time and space requirements are on-topic as long as there's a specific problem or context provided. This wasn't the case here: the user expressed interest in finding out which one was fastest for "gigabytes of data". I tried to get him to provide more detail in hopes we could tease out a good question, but again, he never replied.

  • 1
    I saw the comments and recognize you were trying to work with the poster. My concern is that the question wasn't off-topic to begin with, at least according to the FAQ. I agree the question isn't perfect and the problem description is baggy. It can still be answered without opinions, though. The question's lack of focus and the poster's comments suggest they're new to P.SE and maybe programming. I'd hate to exclude them because we're more focused and would ask the question differently. Jul 14, 2011 at 18:47
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    @Corbin it is, as written, off-topic according to the FAQ: "Please note that the following subjects are considered off-topic here: Which technology is better?" We can assume he wanted more (which is why I tried to tease out a better question), but the question as it is now is hopelessly broad and isn't on-topic here.
    – user8
    Jul 14, 2011 at 18:59
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    I guess we see it differently. I see a request for regex engine features along with speed and memory consumption numbers, all of which can be answered objectively (understanding benchmark numbers are slippery). The poster never asks which engine is better. No worries. Just thought it was worth discussing. Jul 14, 2011 at 19:17
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    @Corbin: they can be answered objectively for a specific benchmark - that is, for a given expression on a given set of data, you'll be able to say which engine completes in the lowest time, uses the least memory, etc. Of course, you can and do end up with designs that trade memory for speed, or speed for memory, or optimize for some expressions at the expense of others, etc... In theory, we could answer his question. Practically-speaking, it's a real crap-shoot as to whether we could give him a useful answer without knowing at least something about what he's trying to do.
    – Shog9
    Jul 15, 2011 at 22:59

The problem with questions phrased like this is they tend to just get everyone posting their favourite X (what ever the subject in question is) and the votes tend to be for your favourite too.

It would probably be more constructive to ask for something that meets your specific criteria. This should get you constructive answers as they (to be upvoted) should solve the problem you have.

That's the thing to remember with Stack Exchange. It works best when you have a specific problem to solve, whether that's why some code doesn't work, or how to drill a hole in a concrete beam, or which plant grows best in sandy soil, or which regex library meets a specific set of requirements.

The only issue could be that your requirements are too general so virtually any regex library would do.

  • 1
    In this case, the criteria appear to be speed and memory use. If I'm interested in benchmark numbers and don't want to run the benchmarks myself, I don't know how else I'd ask the question. The poster doesn't ask for opinions. They ask for numbers. Sure, the question could be tightened up, but I hope we don't throw out questions because they're not phrased exactly the way we would phrase them. Jul 14, 2011 at 17:47
  • The problem with questions phrased like this is they tend to just get everyone posting their favourite X - isn't voting supposed to solve that? Vote facts up, opinions down. ---- meets your specific criteria - water, specs, walking, frozen etc.
    – peterchen
    Aug 10, 2011 at 9:46
  • @peterchen - theoretically, but experience on other Stack Exchange sites has shown that this doesn't happen.
    – ChrisF Mod
    Aug 10, 2011 at 10:07
  • @Chris: in my experience, this depends a lot on the OP and the wording of the question. I agree that disallowing those questions is the option that is easiest to enforce, but I think we can do better.
    – peterchen
    Aug 10, 2011 at 10:14


You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page.

What problem was this person trying to solve? Hard to tell, when the question was all of about two sentences.

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