Why is cast array integer[] <--> text[] is not immutable.

Hi

I'm struggling to understand why this casts is not immutable:

integer[]::text[]
text[]::integer[]

The following are all immutable:

integer::text
text::integer
integer[]::float[]
integer::float

I hit on this while trying to make a gin index which cast from one to the other.

Why does the encapsulation of an array suddenly make this not immutable?

Thanks

Phil Couling <couling(at)gmail(dot)com> writes:
> I'm struggling to understand why this casts is not immutable:

> integer[]::text[]
> text[]::integer[]

Because it's implemented via array_out/array_in rather than any more
direct method, and those are marked stable because they potentially
invoke non-immutable element I/O functions.

regards, tom lane

Thanks

I'm having trouble finding any reference to array_out and array_in in
the documentation.

Is there a way to set a different cast for an array?

Regards

On 9 December 2011 15:09, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Phil Couling <couling(at)gmail(dot)com> writes:
>> I'm struggling to understand why this casts is not immutable:
>
>> integer[]::text[]
>> text[]::integer[]
>
> Because it's implemented via array_out/array_in rather than any more
> direct method, and those are marked stable because they potentially
> invoke non-immutable element I/O functions.
>
>                        regards, tom lane

Phil Couling <couling(at)gmail(dot)com> writes:
> Is there a way to set a different cast for an array?

I think it should work to declare a cast explicitly for the particular
case.

regards, tom lane