Re: implement CAST(expr AS type FORMAT 'template')

On 04/08/2025 07:55, David G. Johnston wrote:
> On Sunday, August 3, 2025, Corey Huinker <corey(dot)huinker(at)gmail(dot)com> wrote:
>
> On Sun, Aug 3, 2025 at 11:36 PM David G. Johnston
> <david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>
>
> I was under the impression that for format to be allowed in
> the expression one of the two data types involved has to be
> text and the other must not be text.
>
>
> I hadn't understood that, but also hadn't thought of a case where
> it might be wanted until just now. What if someone wanted a cast
> from JSONB to their custom type, and the format was a specific
> keypath to extract from the JSONB? It's true that could be
> accomplished by first extracting the keypath and then CASTing that
> expression, but the same is true for text->date, regexing a
> YYYY-MM-DD into the locale default.
>
>
> Feels like the same basic answer.  Create cast has a single (because
> it’s one-way) function accepting between 1 and 3 arguments.  Change it
> to accept between 1 and 4 arguments and the 4th is where the format
> expression gets passed.  If a format expression is present and the
> function doesn’t have a 4th argument, error.

This is my position as well.

+1

--

Vik Fearing