[ruby-core:107370] [Ruby master Feature#18368] Range#step semantics for non-Numeric ranges

Issue #18368 has been updated by zverok (Victor Shepelev).


> the implication is that `range.step(1)` (using `+`) would have different semantics than `range.each` (using succ); I have reservations about that.

Well, it is already so to some extent. Say, with numeric ranges `#step` returns `ArithmeticSequence` and not just Enumerator; and while the difference is subtle, it is there. 

> Also, due to backward compatibility I don't think it's possible to change the behavior of ("a".."z").step(3) so the simple rule of "it just uses +" would suffer from at least one special case.

1. I am not sure about that, actually—how much of the code might use this? (I think there was a way to estimate with gemsearch?..) It is hard for me to imagine the reasonable use case, but I might be wrong.
2. Wouldn't maybe just a clear error message be enough to promptly port all the code affected? It is not the case where something will change semantics silently, it would be a clear and easy to understand exception
3. Worst case, there might be made a special case _only_ for String to preserve old semantics. There were precedents in the past: when `Range#===` was [changed](https://rubyreferences.github.io/rubychanges/2.6.html#range-uses-cover-instead-of-include) to use `#cover?`, the String ranges preserved old behavior... which turned out to be unnecessary and [fixed in the next version](https://rubyreferences.github.io/rubychanges/2.7.html#for-string)

> The idea is that #increment is used for addition but not concatenation. Nothing implicit. If a class has #increment defined that would be used for #step, otherwise it would fall back to using #succ, otherwise it would fail with "can't iterate" just like it does currently. Well, it's just one idea. From the dev meeting notes I also like nobu's idea of just delegating to begin_object#upto.

Both #upto and #increment require *every* gem author to change *every* of their objects' behavior. For that, they should be aware of the change, consider it important enough to care, clearly understand the necessary semantics of implementation, have a resource to release a new version... Then all users of all such gems would be required to upgrade. The feature would be DOA (dead-on-arrival).

The two alternative ways I am suggesting: change the behavior of `#step` or introduce a new method with desired behavior:
1. Easy to explain and announce
2. Require no other code changes to immediately become useful
3. With something like [backports](https://github.com/marcandre/backports) or [ruby-next](https://github.com/ruby-next/ruby-next) easy to start using even in older Ruby version, making the code more expressive even before it would be possible for some particular app/compny to upgrade to (say) 3.2

NB: All examples of behavior from my comments are real `irb` output with monkey-patched `Range#step`, demonstrating how little change will be needed to code outside o the `Range`.

----------------------------------------
Feature #18368: Range#step semantics for non-Numeric ranges
https://bugs.ruby-lang.org/issues/18368#change-96271

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
----------------------------------------
I am sorry if the question had already been discussed, can't find the relevant topic.

"Intuitively", this looks (for me) like a meaningful statement:

```ruby
(Time.parse('2021-12-01')..Time.parse('2021-12-24')).step(1.day).to_a
#                                                         ^^^^^ or just 24*60*60
```
Unfortunately, it doesn't work with "TypeError (can't iterate from Time)".
Initially it looked like a bug for me, but after digging a bit into code/docs, I understood that `Range#step` has an odd semantics of "advance the begin N times with `#succ`, and yield the result", with N being always integer:
```ruby
('a'..'z').step(3).first(5)
# => ["a", "d", "g", "j", "m"]
```

The fact that semantic is "odd" is confirmed by the fact that for Float it is redefined to do what I "intuitively" expected:
```ruby
(1.0..7.0).step(0.3).first(5)
# => [1.0, 1.3, 1.6, 1.9, 2.2] 
```
(Like with [`Range#===` some time ago](https://bugs.ruby-lang.org/issues/14575), I believe that to be a strong proof of the wrong generic semantics, if for numbers the semantics needed to be redefined completely.)

Another thing to note is that "skip N elements" seem to be rather "generically Enumerable-related" yet it isn't defined on `Enumerable` (because nobody needs this semantics, typically!)

Hence, two questions:
* Can we redefine generic `Range#step` to new semantics (of using `begin + step` iteratively)? It is hard to imagine the amount of actual usage of the old behavior (with String?.. to what end?) in the wild
* If the answer is "no", can we define a new method with new semantics, like, IDK, `Range#over(span)`?



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