it carry another example and the solution however I still think that this fuctionality should be avliable in a build-in postgresql function.
This would be a new feature and Postgres only introduces new features in new major version releases. The next major release is 10 and it is the latter stages of development. Not sure if there is a feature freeze on yet or not. In any case it will not be released for production until fall sometime(best guess, I have nothing to do with release schedule).
Not technically frozen but if the implementing patch isn't already in the commit-fest system it isn't getting into 10. All feature freeze means at this point is that anything currently in the commit-fest system that doesn't get committed by that time it going to be punted to 11.
If it did not make it into that release you are looking another year out. So if this is something you need soon, then I would say the solution would be to create your own function using the suggestions provided. If you really want this as a built in, regardless of when it is done I would suggest either filing bug:
Maybe not ideal but we don't have any kind of "feature requests" lists so its either -hackers or -general.
I'd even go so far as to say "-general" is better because you get more eyes on the request for people to give it support and, apparently in this case, finding people to do the leg work of writing a patch.