Martijn van Oosterhout wrote:
On Tue, May 16, 2006 at 10:29:27AM -0700, Don Y wrote:
Given a user defined type foo...
I've created several casts to/from foo and built-in types.
I had adopted a naming convention of:
baz foo_to_baz(foo);
foo foo_from_baz(baz);
But:
<snip>
I don't see how I can do this in my declarations. E.g.,
if I have
baz = {int4, text, float8, ...}
then I end up with several (C) functions all named foo()
but each taking a different argument type (baz). Since
C doesn't support more than a single namespace for functions,
this just won't work.
What am I failing to see, here?
That the name of the function in C doesn't have to be the same as the
name of the function in SQL. You can even define many SQL functions
that all refer to the same C function.
So in your C file yo call them:
cast_foo_to_baz()
and in the SQL you declare as just:
baz()
But what *binds* my C declaration to the corresponding SQL
"CREATE CAST"?
E.g.,
CREATE FUNCTION foo_from_baz(baz)
RETURNS foo
AS '...'
LANGUAGE 'C' IMMUTABLE STRICT;
yet, to support the foo(baz) syntax, I would then need (?)
to continue with:
CREATE CAST (baz AS foo)
WITH FUNCTION foo(baz);
or, do I use:
CREATE CAST (baz as foo)
WITH FUNCTION foo_from_baz(baz);
but then how does the "foo(baz)" syntax originate?
or, is this a built in "feature" of the interpreter?
(In which case, why all the commentary <snip>ed that
tells me to name my functions in this way?)
--don
