Horton

Re: safer node casting

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-01-27T01:29:06Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2016-12-31 12:08:22 -0500, Peter Eisentraut wrote:
>> This is inspired by the dynamic_cast operator in C++, but follows the
>> syntax of the well-known makeNode() macro.

> The analogy to dynamic_cast goes only so far, because we don't actually
> support inheritance.  I.e. in c++ we could successfully cast SeqScanState to a
> PlanState, ScanState and SeqScanState - but with our model only
> SeqScanState can be checked.

Yeah, I was thinking about that earlier --- this can only be used to cast
to a concrete node type, not one of the "abstract" types like Plan * or
Expr *.  Not sure if that's worth worrying about though; I don't think
I've ever seen actual bugs in PG code from casting the wrong thing in that
direction.  For the most part, passing the wrong thing would end up firing
a default: case in a switch, or some such, so we already do have some
defenses for that direction.

			regards, tom lane

Commits

  1. Suppress unused-variable warning.

  2. Make more use of castNode()

  3. Add castNode(type, ptr) for safe casting between NodeTag based types.

  4. Use the new castNode() macro in a number of places.