Negative numbers to DOMAIN casting

[Matija Lesar <matija.lesar@xxxxxxxxx>]

Hi,

I have uint4 domain created like this:
CREATE DOMAIN uint4 AS int8
   CHECK(VALUE BETWEEN 0 AND 4294967295);

If I try to cast negative number to this domain check constraint is not validated:
SELECT -1::uint4, pg_typeof(-1::uint4), 1::uint4, pg_typeof(1::uint4);
 ?column? | pg_typeof | uint4 | pg_typeof
----------+-----------+-------+-----------
       -1 | bigint    |     1 | uint4

Also the pg_typeof returns bigint, but if i do int8 to int2 conversion pg_typeof returns right type:
SELECT pg_typeof(-1::int4::int2);
 pg_typeof
-----------
 smallint

If I put number inside brackets I get check error:
select (-1)::uint4;
ERROR:  value for domain uint4 violates check constraint "uint4_check"

The same error is thrown if I use CAST:
SELECT CAST(-1 AS uint4);
ERROR:  value for domain uint4 violates check constraint "uint4_check"

And also if domain is used in table then check is also working as expected:
CREATE TABLE test(i uint4);
INSERT INTO test VALUES(-1);
ERROR:  value for domain uint4 violates check constraint "uint4_check"

I tested this on PG 9.4 and 9.5.

Is this expected behavior?

Regards,

Matija Lesar