Re: Odd behavior in functions w/ anyarray & anyelement

Tom Lane-2 wrote
> you do have one conceptual error: anyarray to anyelement is supposed
> to return the element type of the input array type. So when you pass
> TEXT[] to this function, the SQL parser decides that the expected
> result type is TEXT.

While this is how it behaves in practice I did not find this described in
the documentation.

There are three relevant psuedo-types in play for this:

anyelement
anyarray
anynonarray

Since the documentation states that anyelement can take on array types the
OP deduced that these signatures:

func(anyelement) returns anyarray
func(anyarray) returns anyelement --including arrays...

if provided array input would be able to echo out the same unmodified array.

if you truly want to enforce an up/down-grading function you would write:

func(anynonarray) returns anyarray
func(anyarray) returns anynonarray

I don't see how the behavior can reasonably change at this point but a
second opinion on the current documentation wouldn't hurt.

http://www.postgresql.org/docs/9.3/interactive/extend-type-system.html#EXTEND-TYPES-POLYMORPHIC

David J.

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