Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
> As another approach, what about storing typeid in typmod?
> (Oid can be assumed to be stored in int32.)
No, it cannot --- you'd be one bit short. The general rule for typmod
is that all negative values are treated as "unspecified". Even if you
managed to find and change every place that assumed that, you'd still
have a failure for -1, which is a perfectly legal value of Oid.
regards, tom lane