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It seems that every week, or almost every day, a new question appears as to why generics in C#/.NET don't support co- and contra-variance (eg here and here). There must be a reason why people aren't finding the questions other people have asked before they post their own ; is there some way we can have a 'standard answer' to covariance questions, or make it easier for people to see other people have the same issues?

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It might be simply that it's a complicated topic and it's difficult to identify a duplicate without understanding what exactly one is asking about – Michael Haren Sep 23 '09 at 22:42
up vote 3 down vote accepted

I've pondered this one myself. It's not unusual to see several covariance/contravariance .NET questions in a single day.

I think the reason this comes up so often is because if you know the terminology, you already know the answer. So the people who end up asking can only do so by simply describing what appears to be strange behavior in their particular use case. There are so many ways to describe the effects without using overlapping keywords, and even if a covariance question did pop up as a suggestion, it's unlikely they would recognize that as a duplicate.

What I would like to do (and have suggested) is that we keep a running list of the "authoritative source" for questions like this, perhaps here on Meta. We can pick the best ".NET covariance" question/answer and consistently point all new ones to that one. It doesn't stop the new questions, but it does canonize the best answer and consolidate the amount of effort that goes into answering.

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The system is already designed to limit duplicate questions.

  • After typing in the title, the system shows you a list of possibly related questions.
  • Over 1,600 users can vote to close duplicate questions, which are then linked to the original question.
  • Many thousands more can leave comments indicating that a question might be a duplicate or flag for moderator attention.

If you see a duplicate post on generics covariance in C#/.NET, pick the best existing answer (as your "standard" answer) and submit a comment with a link to the duplicate question so it can be closed.

I'm not sure what else can be done.

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If a user doesn't understand the concept in the first place or doesn't realize that it's called variance, there is no way he could realize it's a duplicate.

What we should definitely avoid is harassing these types of users for posting duplicates when they may not even realize they are doing so. Simply use your vote to close as a duplicate (if you can) or leave a link as rcartaino suggests. That way, the user will realize the name of the concept of what the underlying problem is and possibly research it a bit from there.

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+1 I think not knowing what something's called is a big factor in dupes generally. – bananakata Sep 24 '09 at 6:07

Seriously, this is a drop in the ocean compared to the 'How do I parse markup with regex?" and "I'm a Javascript and PHP user, please explain the difference?" questions - don't worry about the small stuff.

I wonder if there's an easy way to query the datadump for the most duped question?

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