Did I misunderstand "not constructive"?

Question

Before I post this question I've read

• How is this not constructive? It is duplicate, but very constructive!
• Why was this question closed as not constructive?

I want to get an answer of the truth with my question

Why doesn't Array class expose its indexer directly? [closed]

for design my class in the correct way, but the question get closed by the reason of not constructive.

By the declaration of not constructive:
As it currently stands, this question is not a good fit for our Q&A format.

• According to Bart's answer before:
  We need a good single question related to a practical problem you face ... I want you to ask me a single, self-contained question.
  Thus, should I change the question to
  What should my ToArray method return?
  Would that be better?

We expect answers to be supported by
facts - Does it closed because of there are no answer supported by facts with my question?
references - I can't figure out the references myself, but not implying nobody does. If I can always done it myself, then I would not ask.
or specific expertise - Does it closed because of the question can be answered without specific expertise?
but this question will likely solicit
debate - I'm not expecting that.
arguments - What for?
polling - Opinion poll? No, I expect the truth for the why.
or extended discussion - Then don't extended it, just tell me why.

Answer 1

Yes, to a small extent you have misunderstood. I saw this appear in the re-open queue and spent quite a while working out why it was closed before voting for it to remain that way.

The reason for the closure is explained pretty well in Alexei Levenkov's upvoted comment (my emphasis):

KenKin I vote to close and removing my guess answer why it was done that way. Unless Eric Lippert decides that your question is insanely interesting you have more or less no chance to dig inner reasons of "why". My guess is "no explicit demand for feature and works", but it is just that - guess.

I don't know that I can say it better than that. Unless the designer of the language passes by and decides to answer your question any answer will be a guess, and therefore not very useful for the future. He might, he's a Stack Overflow user but it doesn't seem likely. If he'd like to answer it he can always flag your question for moderator attention to get it reopened.

To go over the points in the close reason; as the question is not answerable by the wider community they cannot supply facts, references or specific expertise. They will instead have to rely on guesswork and discussion.

Answer 2

No, you didn't misunderstand “not constructive”. Your problem is that a large part of the Stack Overflow community does not understand the topic of your question. This is fairly common with language design questions.

Programming language design is a science, albeit a poorly-understood one. There are reasons to make this or that choice, which can have to do with nice theoretical properties, ease of implementation, performance, etc. To complicate matters, language design is also a historical process, so sometimes the reason is “we didn't understand the implications at the time” or “the author of the spec made a typo”. Both kinds of answers call on facts and specific expertise. The former kind is considerably more interesting than the latter, but usually if the asker had known he wouldn't have needed to ask.

Programming language design is on-topic on Stack Overflow because it has a direct impact on programming. It is also on-topic on Computer Science since programming language design is a branch of CS. Unlike the SO community, the CS.SE community understands CS, so I think your question would get a warm reception. However, the CS.SE community is vastly smaller than the SO community. In practical terms, you are far more likely to reach someone who knows the answer on SO than on CS.SE.

(As an advocate and moderator of CS.SE, I hope this will change. Hey, y'all programming language designers, come and join us on Computer Science!)