Re: Domains versus polymorphic functions, redux

On Fri, Jun 3, 2011 at 1:14 AM, Noah Misch <noah(at)leadboat(dot)com> wrote:
> No, there's no need to do that.  The domain "is" an array, not merely something
> that can be coerced to an array.  Therefore, it can be chosen as the polymorphic
> type directly.  Indeed, all released versions do this.

Well, as Bill Clinton once said, "it depends on what the meaning of
the word 'is' is". I think of array types in PostgreSQL as meaning
"the types whose monikers end in a pair of square brackets". We don't
in general have the ability to create a type that behaves "like"
another type. In particular, you can't create a user-defined type
that "is" an array in the same way that a domain-over-array "is" an
array. If we had some kind of type interface facility that might be
possible, but we don't.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company