From: shevegen@...
Date: 2018-05-19T11:17:09+00:00
Subject: [ruby-core:87192] [Ruby trunk Feature#14777] Add Range#offset ?

Issue #14777 has been updated by shevegen (Robert A. Heiler).


I personally prefer the name .offset() here over .shift(), mostly because
my brain remembers Array shift. But the name, while important,
is probably not the most relevant part - more important is what
the method does and the use case.

I think the use case is understandable, e. g. given a range object,
the ruby hacker may want to shift the range easily, up or down, 
without necessarily wanting to create a new range object (even though
that is trivial, too). (Actually, I used the word shift just there ...
so perhaps it is not such a bad name after all ... so perhaps it
should be Range#shift :D ).

I don't know how frequent that use case is; I don't remember having
had a need to modify range objects like that so far, but I can 
understand use cases that exist for it, and after all that would
only give a bit more flexibility to Range, so I am mostly neutral
and somewhat positive on the issue here, so +1/2 up to +1 on it.

(I am using a range here to mildly upvote ... :D )

> Please let me know your thoughts, I can then look to implement
> this properly in C.

I guess it may help if someone from the core team can comment on
the issue here. I myself do not see any problem with the suggested
feature at all but I am not among the core team.

----------------------------------------
Feature #14777: Add Range#offset ?
https://bugs.ruby-lang.org/issues/14777#change-72181

* Author: owst (Owen Stephens)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Hi,

As mentioned in https://bugs.ruby-lang.org/issues/14473#note-17 an addition to Range that we find useful is an `Range#offset(n)` method that adds (or subtracts) `n` to the range, for example:

~~~ruby
(1..10).offset(2)   # => (3..12)
(1...10).offset(1)  # => (2...11)
(1..10).offset(-10) # => (-9..0)
~~~

Similarly to `Range#step` we can support non-Numeric objects if they implement `succ`:
~~~ruby
('a'..'e').offset(2) # => ('c'..'g')
~~~

Alternative names could be `Range#shift` (i.e. shift the elements of the Range up or down) or perhaps `>>`/`<<`:
~~~ruby
(1..10).shift(2) # => (3..12)
(1..10) >> 2 # => (3..12)
(1...10) << 1 # => (0...9)
~~~
However, I don't think the operators are clear enough, so I prefer `offset` or `shift`.

An example pure Ruby implementation is:

~~~ruby
class Range
  def offset(n)
    add_n = ->(x) do
      if x.is_a?(Numeric)
        x + n
      elsif x.respond_to?(:succ)
        n.times { x = x.succ }
        x
      else
        raise ArgumentError, "Can't offset #{x.class}"
      end
    end

    if exclude_end?
      (add_n.call(first)...add_n.call(last))
    else
      (add_n.call(first)..add_n.call(last))
    end
  end
end
~~~

Please let me know your thoughts, I can then look to implement this properly in C.

Regards,
Owen.



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