Though part of why they’re optimized and in the stdlib in the first place is because they’re such common patterns. So without them people would end up writing trivial, unperformant, custom versions. So now that more routines can be moved into the stdlib, they can benefit from optimization later.
(I’m not sure how much the maps routines specifically can be optimized, but stdlib routines routines can generally be more aggressive with unsafe or asm or being coupled to the runtime and its quirks, like bytes.Clone, strings.Builder, etc.)
And there are still plenty of ubiquitous patterns that have been worth including in the stdlib even if they’re usually just simple loops that aren’t very optimizable. Like strings.Index is an easy loop to write, but it comes up so often. Or strings.Cut is basically just an if-statement. But it makes code clearer about its intentions; and optimizations to these down the road benefit everyone.
It’s also true that maps.Keys and maps.Values allocate slices, and that you could avoid this with a loop, but strings.Split, bytes.Split, regexp.FindAll, os.ReadDir return slices and are still worthwhile as opposed to specialized iterators for each one. As with any code, you’re conscious of memory allocations where it counts, and optimize as needed.
In fact, now that generics make it possible, the Go team has discussed using iterators (https://github.com/golang/go/discussions/54245), which would benefit strings.Split even further in addition to all the other slice-returning functions.
So generally you have three options for those slice-returning functions:
- Custom inline loop for some of them. More verbose, will probably be naive and not benefit from stdlib optimizations. - Return a slice and iterate over it with a for loop. Creates allocations that could probably be avoided. - Create a customized iterator for that type. Unfortunately, you can’t really use an ordinary for loop, and extra custom iterators for each type. - Use generic iterators to benefit from the optimized functions and also avoid allocation overhead.
So part of the motivation is that now with generics there’s a variety of further optimizations available even to old functions like strings.Split and regexp.FindAll, in addition to opening up common patterns and optimizations for maps/slices/etc. to be included in the stdlib.