Re: Support for %TYPE in CREATE FUNCTION

Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:

> Altering a function definition in any language other than
> PL/pgSQL really scares me. What do you expect a "C" function
> declared to take a VARCHAR argument to do if you just change
> the pg_proc entry telling it now takes a NAME? I'd expect it
> to generate a signal 11 most of it's calls, and nothing
> really useful the other times.

Good point.

That brings me back to choice 1 in my original message: don't try to
change the function if the table definition changes.

In fact, it's possible to do better. A procedural language could
define a hook to handle table definition changes. The Postgres
backend could define a way to register to receive notification of
table definition changes (this would essentially be an entry in a
table like the proposed pg_depends). The procedural language itself
could then handle the table changes by redefining the function or
whatever.

When defining a function using %TYPE, the procedural language would be
notified that %TYPE was used. It could then record a dependency, if
it was prepared to handle one.

This would permit PL/pgSQL to redefine the function defined using
%TYPE if that seems desirable. It would also permit PL/pgSQL to
behave more reasonably with regard to variables defined using %TYPE.

This would also permit the C function handler to issue a NOTICE when a
C function was defined using %TYPE and the table definition was
changed.

> > If you agree with me on the meta-point, then this is just a quibble
> > about my original patch (which made choice 1 above). If you disagree
> > with me, I'd like to understand why.
>
> The possible SIGSEGV above. Please don't take it personally,
> I'm talking tech here, but it seems you forgot that PL/pgSQL
> is just *one* of many possible languages.

Actually, I don't see this as a disagreement about my meta-point.
Users who use %TYPE must watch out if they change a table definition.
A SIGSEGV is just an extreme case.

> And please forget about a chance to finally track all
> dependencies. You'll never be able to know if some PL/Tcl or
> PL/Python function/trigger uses that function. So not getting
> your NOTICE doesn't tell if really nothing broke. As soon as
> you tell me you can I'd implement PL/Forth or PL/Pascal -
> maybe PL/COBOL or PL/RPL (using an embedded HP48 emulator)
> just to tell "you can't" again :-)

I don't entirely understand this. I can break the system just as
easily using DROP FUNCTION. At some point, I think the programmer has
to take responsibility.

I return to the question of whether the Postgres development team is
interested in support for %TYPE. If the team is not interested, then
I'm wasting my time. I'm seeing a no from you and Tom Lane, and a
maybe from Bruce Momjian.

Ian