> Seems like 5 and 6 need to be merged - the chosen type is the first one > that all subsequent types can be implicitly cast to. We do not guarantee > that previous types will be implicitly convertible to this type. > In pseudo-code: > else if (can_coerce(n->p)) continue /* matches when pispreferred */ > else if (can_coerce(p->n)) "change chosen type" > else continue /* but now we expect a runtime implicit cast not found error > */
This formulation fails to account for the pispreferred check, though. The pseudo-code would be correct if you made the first line be
else if (pispreferred || can_coerce(n->p)) continue
but then it doesn't map neatly to a description that fails to mention preferred-ness. (Note that this would be simpler if we could assume that pispreferred implies that there is a cast from every other category member type to p. But there are counterexamples.)
I was making that assumption.
In the pseudo-code:
else if (pispreferred) continue; /* never move away from a preferred type */
{the rest of the else ifs from above}
In the docs:
5. If the first non-unknown type is a preferred type it is chosen, otherwise it is made a candidate, and then,
6. each subsequent type is compared to the current candidate, with a new candidate being chosen only when there exists a non-mutal implicit cast to the new type.
6a. If at any point a preferred type is made a candidate then it will be chosen.
