Tom Lane wrote:
The null Datum itself obviously doesn't carry that info, but the
expression tree does, and there are provisions for letting functions
retrieve that info --- see get_fn_expr_rettype and get_fn_expr_argtype.

Hmm. I vaguely remember that there was some feeling that the PLs wouldn't always fill out the FmgrInfo struct, but perhaps that was just the case with I/O functions.

... could we have a special rule that would look for e.g. a regtype as the first parameter if the return type is generic and there are no generic parameters?

I thought about that too but don't like it much.  The problem is mainly
that it can only work for a constant regtype parameter.

OK, I give up. :) Why?



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