Re: Domains versus polymorphic functions, redux

On May 24, 2011, at 11:30 AM, Tom Lane wrote:

> Well, if they actually were first-class types, they probably wouldn't
> be born with an implicit cast to some other type to handle 99% of
> operations on them ;-).  I think the hard part here is having that cake
> and eating it too, ie, supporting domain-specific functions without
> breaking the implicit use of the base type's functions.

Yeah.

> I guess that the question that's immediately at hand is sort of a
> variant of that, because using a polymorphic function declared to take
> ANYARRAY on a domain-over-array really is using a portion of the base
> type's functionality.  What we've learned from bug #5717 and the
> subsequent issues is that using that base functionality without
> immediately abandoning the notion that the domain has some life of its
> own (ie, immediately casting to the base type) is harder than it looks.

Well, in the ANYELEMENT context (or ANYARRAY), what could be lost by "abandoning the notion that the domain has some life of its own"?

Best,

David