Re: argtype_inherit() is dead code

Are you saying that the code was supposed "unflatten" the
arguments of a function into a possible composite type taking into
consideration the possible inheritance information of the
composite type?

elein

On Fri, Apr 15, 2005 at 08:04:36PM -0400, Tom Lane wrote:
> In parse_func.c there are routines argtype_inherit() and
> gen_cross_product() that date from Berkeley days. The comments
> explain their reason for existence thus:
>
> * This function is used to handle resolution of function calls when
> * there is no match to the given argument types, but there might be
> * matches based on considering complex types as members of their
> * superclass types (parent classes).
> *
> * It takes an array of input type ids. For each type id in the array
> * that's a complex type (a class), it walks up the inheritance tree,
> * finding all superclasses of that type. A vector of new Oid type
> * arrays is returned to the caller, listing possible alternative
> * interpretations of the input typeids as members of their superclasses
> * rather than the actually given argument types. The vector is
> * terminated by a NULL pointer.
> *
> * The order of this vector is as follows: all superclasses of the
> * rightmost complex class are explored first. The exploration
> * continues from right to left. This policy means that we favor
> * keeping the leftmost argument type as low in the inheritance tree
> * as possible. This is intentional; it is exactly what we need to
> * do for method dispatch.
> *
> * The vector does not include the case where no complex classes have
> * been promoted, since that was already tried before this routine
> * got called.
>
> I realized that this is effectively dead code: although it can be
> executed, it can never produce any useful results. The reason is that
> can_coerce_type() already knows that inherited rowtypes can be promoted
> to their parent rowtypes, and it considers that a legal implicit
> coercion. This means that any possible function matches based on
> promoting child rowtypes to ancestors were found in func_get_detail()'s
> first pass. If there is exactly one match then it will be taken as
> the correct answer and returned without calling argtype_inherit().
> If there is more than one match then func_get_detail() will fail
> (return FUNCDETAIL_MULTIPLE), again without calling argtype_inherit().
> The only way to reach argtype_inherit() is if there are *no* ancestor
> matches, which means that the function is a very expensive no-op that
> we execute just before throwing an error.
>
> I'm strongly tempted to just rip out argtype_inherit() and
> gen_cross_product(). Even if we suppose that we might want to resurrect
> the claimed functionality someday, I don't think it could be made to
> work this way. You'd have to put the knowledge into
> func_select_candidate() instead, else there'd be very weird interactions
> with the heuristics for resolving non-complex input argument types.
>
> Thoughts?
>
> regards, tom lane
>
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