[ruby-core:107354] [Ruby master Feature#18368] Range#step semantics for non-Numeric ranges

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


> Here's one idea: how about adding an #increment(n) method. For Numeric, Float, Time, Date, it would be an alias to +. For String it would be equivalent to doing succ n times. So Range#step would have the semantics of using begin.increment(step) iteratively.

What about other, non-core classes? Will we have implicitly defined `Object#increment` to handle them, and if so, how it is defined? Or each and every library should define their own `#increment`, and if it doesn't, the range iteration just fails?

In general, I believe this approach would render the feature virtually unusable. 

On the other hand, "It just uses `+`" follows the principle of least surprise, and is easy to explain and document. It is also totally easy to grasp why in cases where `+` is defined as concatenation, the result is the way it is (the same way that result of `('A'..'aa').to_a` might be "somewhat surprising" at first, but is easy to explain in hindsight).

In general, what I am trying to do here is to make the semantics more intuitive, not more complicated to tailor some special case.

PS: I might even suppose a reasonable use of the new proposed `step` with strings. For example, in Markdown markup language, the level of the header is designated by the number of `#` before it. So, one might do something like 
```ruby
PREFIXES = (''..).step('#').take(7)
# => ["", "#", "##", "###", "####", "#####", "######"]

# ...or even just 
PREFIXES = (''..'######').step('#').to_a
# => ["", "#", "##", "###", "####", "#####", "######"]

# and then use it like 
def render_header(h)
  "#{PREFIXES[h.level]} #{h.text}"
end
```
Would this be an unreadable crime against common sense? I'd say not. YMMV.
(I am not saying you can't do `'#' * h.level` or that it is worse. I am just saying that nothing "weird" seems to be in the semantics of `Range#step` even in the String case.)

----------------------------------------
Feature #18368: Range#step semantics for non-Numeric ranges
https://bugs.ruby-lang.org/issues/18368#change-96253

* 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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