Re: JSON for PG 9.2

On Tue, Dec 13, 2011 at 5:22 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> On 12/12/2011 03:54 PM, Robert Haas wrote:
>>> There are way too many places that assume that the typmod can
>>> just be discarded.  I don't think that's going to fly, because
>>> =(text,text) probably has different semantics from =(json,json).
>
>> And certain places where they are not allowed at all, I think (unless I
>> am misremembering the early debates about enum types and output functions).
>
> Yeah.  The current system design assumes that typmod specifies a
> constraint of some sort.  It is not possible to use it to change the
> semantics of the datatype.  The most obvious way in which this is true
> is that selection of which operators and functions to apply to values
> does not consider typmod of the values.  This is not something we should
> lightly revisit.  We don't even have a handle on how to make domains
> behave differently from their underlying datatypes, and those *do* have
> their own type OIDs.  Injecting typmod into the algorithm seems like a
> disaster from here.

I'm glad I didn't think of doing that before then.

Can we agree some wording to put into the docs? Sounds like some clear
warnings are needed.

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