Re: feature request - datum_compute_size and datum write_should be public

On Feb 1, 2012, at 12:45 AM, Pavel Stehule wrote:
>>> I looked to sources and I found a some useful routines for people who
>>> write extensions and probably PL too.
>>
>>> There are datum_compute_size and datum_write from range_types.c. These
>>> routines can be used in PL libs and maybe in other places.
>>
>>> Should be these routines moved to varlena.c and be public?
>>
>> Why?  It is not common for types to contain other types, and it
>> certainly isn't likely to happen without needing lots of other
>> infrastructure --- the existing examples are arrays, records, and
>> rangetypes, and all of those come with lots of baggage.  And there
>> are a number of choices in those functions that are pretty specific to
>> rangetypes, as illustrated by the fact that they're not already sharing
>> code with either arrays or records.
>
> For example I can use this code in my implementation of set of enum
> (enumset datatype) because I have to wrap a array sometimes (I reuse a
> array infrastructure).
>
> In orafce I can use this code for serialisation and deserialisation
> Datums - it is used more times there

I'm not certain this in what  Pavel is referring to, but I have often wished that I could pass something like an array
intoa function and have the function tell me exactly how much space that would require on-disk. It's pretty easy to
figurethat out for things like varchar and numeric, but doing so for arrays or composite types requires pretty detailed
knowledgeof PG internals. 
--
Jim C. Nasby, Database Architect                   jim@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net