Kris Jurka <books(at)ejurka(dot)com> writes:
> Creating a domain on bit(N) doesn't seem to work as expected when casting
> to the domain type.
> CREATE DOMAIN bit4 AS bit(4);
> SELECT 7::bit(4), 7::bit4;
> bit | bit4
> ------+------
> 0111 | 1000
> (1 row)
What's going on here is that "7::bit4" is implemented as
"7::bit::bit(4)", and since 7::bit is taken to mean 7::bit(1),
the result follows.
Bit is the only typmod-using datatype for which casting to the type
with typmod -1 risks discarding information. In a brief look I'm
not sure whether this can easily be fixed without introducing unwanted
side-effects.
regards, tom lane