[ruby-core:94990] [Ruby master Feature#16021] floor/ceil/round/truncate should accept a :step argument

Issue #16021 has been updated by Dan0042 (Daniel DeLorme).


> `Time.now.floor(step: 3600)` doesn't work well with leap seconds.

```ruby
n =3D (Time.now.to_i / 86000).floor * 86400
ENV["TZ"] =3D "UTC";       Time.at(n) #=3D> 2019-12-13 00:00:00 +0000
ENV["TZ"] =3D "right/UTC"; Time.at(n) #=3D> 2019-12-12 23:59:33 +0000
```

Wow. I thought that leap seconds were handled by the OS by repeating the sa=
me unix timestamp twice, or freezing or fudging time. To think that the TZ =
would change the meaning of a timestamp in such a way... I learned somethin=
g quite interesting today. (Thanks #8885 btw)

> For float values, we could suffer from errors. =


That's always the case for any float operations right? `12.3456.floor(4)` =
=3D> 12.3455
It's possible to fix precision errors (for floor/ceil), but is it desirable?

But since the proposal is rejected for Time, it's much less relevant for Nu=
meric in general. It's ok to close this.


----------------------------------------
Feature #16021: floor/ceil/round/truncate should accept a :step argument
https://bugs.ruby-lang.org/issues/16021#change-81616

* Author: Dan0042 (Daniel DeLorme)
* Status: Feedback
* Priority: Normal
* Assignee: =

* Target version: =

----------------------------------------
These rounding methods currently accept a number of (decimal) digits, but a=
 more general mechanism would allow rounding to the nearest =BC, multiple o=
f 5, etc.
Equivalent to e.g. `((num / step.to_f).round * step)`

``` ruby
12.3456.floor(step: 0.2) #=3D> 12.2
12.3456.round(step: 0.2) #=3D> 12.4
12.3456.floor(step: 0.2) #=3D> 12.4
12.3456.floor(step: 0.2) #=3D> 12.2
```

IMHO this should also apply to Time#floor/round/ceil

``` ruby
Time.now.floor(step: 3600) #=3D> current hour
Time.now.round(step: 3600) #=3D> nearest hour
Time.now.ceil(step: 3600)  #=3D> next hour
```

We can also consider that instead of `:step` , `:by` or `:to` might be quit=
e readable.

``` ruby
12.3456.round(by: 0.2) #=3D> 12.4
12.3456.round(to: 0.2) #=3D> 12.4
```



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