From: | Thomas Lockhart <lockhart(at)alumni(dot)caltech(dot)edu> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Hackers List <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Operators and commutation |
Date: | 2000-12-01 07:19:02 |
Message-ID: | 3A2750E6.C5751C3E@alumni.caltech.edu |
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Lists: | pgsql-hackers |
Tom, can you refresh my memory on the preferred way to define
"commutative operators" for operators with mixed input types? For
example, I want to define a new operator to add an interval to a time.
Do I need to fully implement the commutative function which adds a time
to an interval, or is there another way?
I used to have a cheat interpretation of commutation during operator
matching in the parser (which allowed a mixed-type operator to refer to
itself as its commutator, and the parser would then flip the arguments
around to match up), but I recall that you took this out to reinforce
the purity of the interpretation of commutation in the table flags. So
what is the best way to do this now?
- Thomas
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