Re: Proposal: casts row to array and array to row

2011/10/11 Merlin Moncure <mmoncure(at)gmail(dot)com>:
> On Tue, Oct 11, 2011 at 3:40 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
>> Hello
>>
>> A current limits of dynamic work with row types in PL/pgSQL can be
>> decreased with a possible casts between rows and arrays. Now we have a
>> lot of tools for arrays, and these tools should be used for rows too.
>>
>> postgres=# \d mypoint
>> Composite type "public.mypoint"
>>  Column │  Type   │ Modifiers
>> ────────┼─────────┼───────────
>>  a      │ integer │
>>  b      │ integer │
>>
>> postgres=# select cast(rmypoint '(10,20) as int[]);
>>   array
>> ────────────
>>  {10,20}
>> (1 row)
>>
>> postgres=# select cast(ARRAY[10,20] AS mypoint);
>>  mypoint
>> ─────────
>>  (10,20)
>> (1 row)
>>
>> What do you think about this idea?
>
> Not sure what it buys you over the syntax we already have:
>
> select row(foo[1], bar[2]);
> select array[(bar).a, (bar).b];

You can do it manually for known combinations of rowtype and
arraytype. But proposed casts do it generally - what has sense mainly
for plpgsql functions or some sql functions.

>
> Also, in my coding of composite types, homogeneously typed rows don't
> really come up that often...

you can use everywhere text type.

When I wrote http://stackoverflow.com/questions/7711432/how-to-set-value-of-composite-variable-field-using-dynamic-sql/7722575#7722575
then I had to do lot of string operations. Proposed casts
significantly do this simply - and it is enought general for general
usage.

Pavel

>
> merlin
>