Re: Domains versus polymorphic functions, redux

Robert Haas <robertmhaas@gmail.com> writes:
> The real crux of the issue here is: under what circumstances should we
> look through the domain wrapper around an underlying type, and under
> what circumstances should we refrain from doing so?

That's half of it.  The other half is: when we *do* look through the
wrapper, is that equivalent to having implicitly inserted a downcast
to the base type, so that the results are now indistinguishable from
having given a base-type value to begin with?  Or is the expression's
behavior still affected by the fact of having given a domain value,
and if so, how exactly?

I assert that matching a domain-over-array to an ANYARRAY parameter
certainly involves having "looked through the wrapper".  It's
considerably fuzzier though what should happen when matching a domain
to ANYELEMENT.
        regards, tom lane