[ruby-core:98180] [Ruby master Feature#16818] Rename `Range#%` to `Range#/`

Issue #16818 has been updated by mrkn (Kenta Murata).


I borrowed the idea of `Range#%` from numo-narray.

When I first looked `Range#%` in numo-narray, I felt it is natural.
I refer one expression from the above example sawa showed:

> ```
> (5..14).group_by.with_index{|_, i| i % 3}
> # => {0=>[5, 8, 11, 14], 1=>[6, 9, 12], 2=>[7, 10, 13]}
> ```

You can see the 0th array of the resulting hash above equals to `((5..14)%3).to_a`:

```
((5..14)%3).to_a == (5..14).group_by.with_index{|_, i| i % 3}[0]
# => true
```

----------------------------------------
Feature #16818: Rename `Range#%` to `Range#/`
https://bugs.ruby-lang.org/issues/16818#change-85420

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
----------------------------------------
`Range#%` was introduced as an alias of `Range#step` by 14697, but it is counter-intuitive and confusing.

Iteration in the following:

```ruby
((5..14) % 3).each{|i| p i}
#>> 5
#>> 8
#>> 11
#>> 14
```

is not based on `x % y` in any sense. In fact, actually applying `% 3` to the selected elements returns a unique value `2`, and it is not obvious how this is related to the iteration.

```ruby
[5, 8, 11, 14].map{|i| i % 3}
# => [2, 2, 2, 2]
```

Rather, the concept seems to be based on `/`. Applying `/ 3` to the relevant elements returns a sequence `1, 2, 3, 4`.

```ruby
[5, 8, 11, 14].map{|i| i / 3}
# => [1, 2, 3, 4]
```

Hence, `(5..14).step(3)` can be interpreted like this: Iterate over the [equivalence class](https://en.wikipedia.org/wiki/Equivalence_class) (quotient set) of range `5..14` yielded by `/ 3`.

Notice that the number of elements in `[5, 8, 11, 14]` is 4, which is `(14 - 5 + 1) / 3.0).ceil`, but is not related to `%`.

So I propose that the alias of `Range#step` should be `Range#/`, and `Range#%` should be deprecated as soon as possible before its use accumulates:

```ruby
((5..14) / 3).each{|i| p i}
#>> 5
#>> 8
#>> 11
#>> 14
```

---

P.S.

And if `Range#%` were to be introduced at all, I would rather expect it to behave like the following:

```ruby
((5..14) % 3).each{|i| p i}
#>> 5
#>> 6
#>> 7
```

which is why I claimed above that the current `Range#%` is confusing.



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>