Whatever you think the best name for it is, it's still missing from the library.
Plus it's in the class of things that's pretty easy to implement yourself now. There's always a huge supply of "but the library could just compose these two things for me". If you stick them all in things get bloated. You could literally have written it in the time it took to write the complaint. You got 80% of the way there as it is, I just tweaked your code a bit to turn it into an iterator: https://go.dev/play/p/agBGl_rT7XS
It does not. slices.Sorted accepts an iterator, but returns a slice.
Like the earlier comments point out, Go tries its best to give a reasonable idea of what kind of complexity is involved at the API level. slices.Sorted returning an iterator would mask that. By returning a slice, it makes clear that the entire collection of data needs to be first iterated over as the parent described.
I think returning an iterator is acceptable, the docs could explain the expense of the operation, and the implementation could change in the future as needed. But that does hide some complexity.
If it ought to return a slice of entries, that opens up new problems. What is an entry? A two-member generic struct? Ok, fine, but then how do I ergonomically iterate over them, pulling out both members? There's no clear solution to that problem yet.
Sure, there may be some edge case situations, like where you are dealing with someone else's code where you don't have control over the structures you've been given, but:
1. The standard library doesn't appeal to edge cases.
2. The "noiser" solutions to deal with the edge case serve as a reminder that you aren't working in the optimal space.
But I'd also suggest that if you think you need sorted keys, double-check. I program an awful lot of things without sorted keys, and I am quite aware of the issues around sorting, and I suspect without proof that a lot of people swearing by sorted maps are imposing false ordering requirements on their code more often than they realize. The ideal solution is not need order at all.
(I am especially suspicious of extensive use of maps where the keys are sorted by insertion order. That smells... antipatternish to me.)
Whether in particular cases, a properly ordered data structure (like a tree) should be used instead, is a valid question to ask, and thanks to the custom iterators, it'll now be more ergonomic to use. But if I usually use a particular map for its O(1) operations and only occasionally iterate over the whole thing, yet need consistent iteration order, then the built-in map still seems like the right choice, and having a standard way to iterate it is a reasonable request.
That is literally the edge case example I gave. Perhaps there is a better way to describe it than "edge case", but semantics is a silly game.
> then the built-in map still seems like the right choice, and having a standard way to iterate it is a reasonable request.
And, indeed, the standard library provides slices.Sorted(maps.Keys(m)) for exactly that. Ergonomic enough, while making the compromise being made reasonably explicit to help with readability – which is far more important than saving a few keystrokes. If typing is your bottleneck, practice will quickly solve that problem.
However, as examined in a sibling thread, there doesn't seem to actually be any missed optimization which could potentially be applied here.
Even ignoring that in the most common case the map isn't the right structure to begin with, what even is the general case for the situations that remain? You mentioned the marshalling of arbitrary data case, but in that case you also have reflection details to worry about, and which you can optimize for with a custom implementation, and thus wouldn't likely use the built-in anyway. A sibling thread discussed the cache benefits of colocating the values with the keys if a map is exceedingly small, but as soon as the map is of any reasonable size the added overhead of the values is almost certainly going to blow the cache even where the keys alone might still fit.
All of which is to say that the best approach is highly context dependent. How do you even begin to choose which is the general case if you were to include such a function?
if a function returns an iterator, it should be iterating the input. thats impossible in this situation. you'd need to loop the entire map, then return an iterator that tricks the user into thinking they are getting better performance when they are getting the worst possible performance.
But a good demonstration of why this kind of thing isn't a good fit for the standard library.
But I've got plenty of cases where this in fact is cache friendly, because the entire map fits into L2 or even L1 anyhow because it's going to have maybe 4 keys in its lifetime. Not every map has fifty million values in it. I'm always keeping at least a little bit of track about such details when I'm using maps.
First, it would save one line of code (v := m[k]). Second, it would also allow an optimization. When iterating a map directly, you have both the key and the value at the same time. However, since we iterate only the keys here, we then have to look up the value anew for each key. That takes extra time and, for large maps, will thrash the CPU cache.
So the following would be both fewer lines of code and faster:
for k, v := range maps.Sorted(m) {
// do something with k and v
}