[ruby-core:97400] [Ruby master Misc#16678] Array#values_at has unintuitive behavior when supplied a range starting with negative index

Issue #16678 has been updated by shevegen (Robert A. Heiler).


Actually .values_at() confused me when I tried to use my go-to method for 
obtaining a slice from an Array:

    a[3..5] # => [4, 5]

There I wondered why it did not return the same. :-)

But anyway; I believe the question is what -1 refers to. It should be the 
last entry, right? Ok, so what should the 3 indicate? I think you reason
that it should refer to the fourth entry (I think ... if an Array count
begins at 0, then 3 would refer to the fourth entry). So from that point
of view I actually do not even disagree with you; perhaps I may have 
missed some other explanation. (There is probably another explanation;
I think this has come up in the past too. I forgot the explanation,
though, if there was one.)

Personally I will stick with [] an leave .values_at() to others. I am
just so used to [] there. ;-)


----------------------------------------
Misc #16678: Array#values_at has unintuitive behavior when supplied a range starting with negative index
https://bugs.ruby-lang.org/issues/16678#change-84530

* Author: prajjwal (Prajjwal Singh)
* Status: Open
* Priority: Normal
----------------------------------------
Consider the following:

``` ruby
# frozen_string_literal: true

a = (1..5).to_a

p a.values_at(3..5) # => [4, 5, nil]
p a.values_at(-1..3)  # => []
```

When the range begins with a negative `(-1, 0, 1, 2, 3)`, it returns an empty array, which surprised me because I was expecting `[1, 2, 3, 4]`.

The argument for this is that it cold be confusing to allow this because the index `-1` could refer to the last argument and it would be unintuitive to return an array `[5, 1, 2, 3, 4]` with jumbled values.

The argument against it is that it makes perfect sense to account for this case and return `[nil, 1, 2, 3, 4]`.

Opening a dialog to see what others think of this.




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