P0157 and Advisory information return values.

[Nicol Bolas]

P0157 discusses various methods for handling "disappointment" (aka: errors). However, I was wondering about a particular condition that it refers to, which is something that I have had no experience with: "Advisory information." This is apparently a return value that represents how you may want to use the API/service/etc in the future. A hash table getting too full or concurrent APIs being "under contention" were explicit examples.

Does anyone have any experience with an API that provides such advise as return values from functions? I know of APIs that can provide such information upon request, what I would call "out-of-band" reporting. But I have not had any experience with APIs that actually offer advice as part of a function's API.