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Re: ANSI-strict pointer aliasing rules

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, Martijn van Oosterhout <kleptog(at)svana(dot)org>, mark(at)mark(dot)mielke(dot)cc, Andrew Dunstan <andrew(at)dunslane(dot)net>, Taral <taralx(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: ANSI-strict pointer aliasing rules
Date: 2006-04-27 19:25:45
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Lists: pgsql-hackers
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Greg Stark <gsstark(at)mit(dot)edu> writes:
> > There are other ways of achieving the same thing. Structs containing a union
> > for the subclass fields for example.
> Doesn't achieve the same thing, unless you mandate that every part of
> the system use the identical massively-overloaded union struct to refer
> to every node.  

Are you saying it's important to preserve the ability for modules to add new
node types without notifying the rest of the code? I thought all the node
types were defined in a single header file currently anyways.

> That would (a) defeat the purpose of extensibility, and (b) make the code
> more error prone not less so (since it'd be notationally easy to refer to a
> field that's not actually present in the given node subtype).

You could use a local pointer to be preserve the existing model of a single
point where the decision is made. That could be encapsulated in a macro that
included an assertion to verify the type tag.

It would be pretty cool to have a type-safe codebase. It just seems like too
an awful lot of work for a mostly aesthetic improvement.


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