TODO item: Accept aliases for values in ROW(...) constructor

Hi all

Especially with the introduction of json support, but also in the past
with hstore and other things, I've sometimes found myself wishing I
could provide aliases in an anonymous row constructor, e.g.

ROW(x AS something, y AS somethingelse)

The same thing can be done using a scalar subquery wrapping a
subquery-in-FROM returning a single row, but it's pretty ugly:

(SELECT r FROM (SELECT x AS something, y AS somethingelse) r)

That's what I've done to produce json a lot, though, and will need to
continue to do so until 9.4's json_build_object etc are in the wild.

While that'll solve the need for json, I'm sure others will come up. So
in case someone feels like exploring the parser a little, does it seem
reasonable to add ROW(...) with aliases to the TODO?

Or, alternately, and perhaps more generally useful, allow rowtype
specifications for anonymous records outside function-call context, like:

ROW(x1,y1) AS r(x integer, y integer)

Related:

http://stackoverflow.com/q/13227142/398670

--
Craig Ringer http://www.2ndQuadrant.com/
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