From: "zverok (Victor Shepelev)" Date: 2022-01-30T14:12:34+00:00 Subject: [ruby-core:107365] [Ruby master Feature#18368] Range#step semantics for non-Numeric ranges Issue #18368 has been updated by zverok (Victor Shepelev). Some clarifications after rereading the corresponding [dev.meeting log](https://github.com/ruby/dev-meeting-log/blob/master/DevMeeting-2022-01-13.md#feature-18368-rangestep-semantics-for-non-numeric-ranges-zverok): **My proposal is not about `Time`, but about generic behavior.** Besides `Time`, realistic, existing, types to handle are at least: * `Date` and `DateTime` * and any other date-alike/time-alike objects of third-party gems, say, "time-of-day" object (gem [tod](https://github.com/jackc/tod)): ```ruby require 'tod' require 'active_support/all' (Tod::TimeOfDay.parse("8am")..Tod::TimeOfDay.parse("10am")).step(30.minutes).to_a #=> [#, #, #, #, #] ``` * ...or `ActiveSupport::Duration` itself: ```ruby (1.minute..20.minutes).step(2.minutes).to_a #=> [1 minute, 3 minutes, 5 minutes, 7 minutes, 9 minutes, 11 minutes, 13 minutes, 15 minutes, 17 minutes, 19 minutes] ``` * Matematical vectors and matrices: ```ruby require 'matrix' (Vector[1, 2, 3]..).step(Vector[1, 1, 1]).take(3) #=> [Vector[1, 2, 3], Vector[2, 3, 4], Vector[3, 4, 5]] ``` * Quantities with measurement units: ```ruby require 'unitwise' (Unitwise(0, 'km')..Unitwise(1, 'km')).step(Unitwise(100, 'm')).map(&:to_s) #=> ["0 km", "1/10 km", "1/5 km", "3/10 km", "2/5 km", "0.5 km", "3/5 km", "7/10 km", "4/5 km", "9/10 km", "1 km"] ``` * ...any other custom type with meaningful semantic of addition **I believe that simple and explicable semantics of reusing `+` is enough**. It creates a good quick intuition of "what would happen", which requires no exceptions and clarifications. We already following similar approach in different places: for example, `('2.7'..'3.1') === '3.0.1'` "just works" without any additional nuances, even if `('2.7'..'3.1').to_a` wouldn't produce `3.0.1` as one of the "range contained elements". For another close example, things like `('5'..'a').to_a` "just work", even if rarely semantically sound, because they follow a simple rule of "just uses `#succ`, however it is defined". Finally, as stated above, **I don't think that _unexpected yet useful_ results of simple intuitions are bad**���vice versa, it is funny and enlightening that this "just works as expected": ```ruby (''..'######').step('#').to_a # => ["", "#", "##", "###", "####", "#####", "######"] ``` ---------------------------------------- Feature #18368: Range#step semantics for non-Numeric ranges https://bugs.ruby-lang.org/issues/18368#change-96266 * 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)`? -- https://bugs.ruby-lang.org/ Unsubscribe: