Re: [HACKERS] [PATCH] Generic type subscripting

> On Wed, Dec 30, 2020 at 02:45:12PM +0100, Dmitry Dolgov wrote:
> > On Sat, Dec 26, 2020 at 01:24:04PM -0500, Tom Lane wrote:
> >
> > In a case like jsonpath['...'], the initially UNKNOWN-type literal could
> > in theory be coerced to any of these types, so you'd have to resolve that
> > case manually.  The overloaded-function code has an internal preference
> > that makes it choose TEXT if it has a choice of TEXT or some other target
> > type for an UNKNOWN input (cf parse_func.c starting about line 1150), but
> > if you ask can_coerce_type() it's going to say TRUE for all three cases.
> >
> > Roughly speaking, then, I think what you want to do is
> >
> > 1. If input type is UNKNOWNOID, choose result type TEXT.
> >
> > 2. Otherwise, apply can_coerce_type() to see if the input type can be
> > coerced to int4, text, or jsonpath.  If it succeeds for none or more
> > than one of these, throw error.  Otherwise choose the single successful
> > type.
> >
> > 3. Apply coerce_type() to coerce to the chosen result type.
> >
> > 4. At runtime, examine exprType() of the input to figure out what to do.
>
> Thanks, that was super useful. Following this suggestion I've made
> necessary adjustments for the patch. There is no jsonpath support, but
> this could be easily added on top.

And the forgotten patch itself.