Why does array_position_common bitwise NOT an Oid type?

Hi,

I was puzzled to see the following code:

my_extra->element_type = ~element_type;

It looks quite wrong, but if its right then I think it needs a comment
to explain it. I don't see any in the area which mentions it. My best
guess would be that it's using this to know if the type data has been
cached, but then why would it not use InvalidOid for that?

-- 
 David Rowley                   http://www.2ndQuadrant.com/
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