Bug #18247
Updated by Eregon (Benoit Daloze) over 2 years ago
There are weird results for `Array#slice` or `Array#[]` with argument of type `Enumerator::ArithmeticSequence`.
Particularly most results with negative steps are weird. For example:
```ruby
@array = [0, 1, 2, 3, 4, 5]
@array.slice((2..).step(-1)) # => [2, 1, 0]
@array.slice((2..).step(-2)) # => [2, 0]
@array.slice((2..).step(-3)) # => [2]
@array.slice((2..).step(-4)) # => [0] # ??? I'd have expected [2]
@array.slice((-3..).step(-1)) # => [3, 2, 1, 0]
@array.slice((-3..).step(-2)) # => [3, 1]
@array.slice((-3..).step(-3)) # => [3, 0]
@array.slice((-3..).step(-4)) # => [3]
@array.slice((-3..).step(-5)) # => [0] # ??? I'd have expected [3]
```
Have a look at these examples with "beginless" ranges and negative steps.
Particularly the ones exluding the end value (`...`) seem wrong:
```ruby
@array = [0, 1, 2, 3, 4, 5]
## end with zero index
@array.slice((..0).step(-1)) # => [5, 4, 3, 2, 1, 0]
@array.slice((...0).step(-1)) # => [5, 4, 3, 2, 1, 0]
@array.slice((..0).step(-2)) # => [5, 3, 1]
@array.slice((...0).step(-2)) # => [5, 3, 1]
@array.slice((..0).step(-10)) # => [0]
@array.slice((...0).step(-10)) # => [0]
## end with positive index
@array.slice((..3).step(-1)) # => [5, 4, 3]
@array.slice((...3).step(-1)) # => [5, 4, 3]
@array.slice((..3).step(-2)) # => [5, 3]
@array.slice((...3).step(-2)) # => [5, 3]
@array.slice((..3).step(-10)) # => [3]
@array.slice((...3).step(-10)) # => [3]
## end with negative index
@array.slice((..-2).step(-1)) # => [5, 4]
@array.slice((...-2).step(-1)) # => [5, 4]
@array.slice((..-2).step(-2)) # => [5]
@array.slice((...-2).step(-2)) # => [5]
@array.slice((..-2).step(-10)) # => [4]
@array.slice((...-2).step(-10)) # => [4]
```
Finally, some examples where the range is "inverted".
Particularly, the results for the ones excluding the end value (`...`) look strange.
But all examples seem weird, but I might not understand the concept of arithmetic sequence in depth.
```ruby
@array = [0, 1, 2, 3, 4, 5]
# start and end with positive index
@array.slice((3..1).step(-1)) # => [3, 2, 1]
@array.slice((3...1).step(-1)) # => [2, 1]
@array.slice((3..1).step(-2)) # => [3, 1]
@array.slice((3...1).step(-2)) # => [2]
@array.slice((3..1).step(-10)) # => [1]
@array.slice((3...1).step(-10)) # => [1]
# start with negative index, end with positive index
@array.slice((-2..1).step(-1)) # => [4, 3, 2, 1]
@array.slice((-2...1).step(-1)) # => [3, 2, 1]
@array.slice((-2..1).step(-2)) # => [4, 2]
@array.slice((-2...1).step(-2)) # => [3, 1]
@array.slice((-2..1).step(-10)) # => [1]
@array.slice((-2...1).step(-10)) # => [1]
# start with positive index, end with negative index
@array.slice((4..-4).step(-1)) # => [4, 3, 2]
@array.slice((4...-4).step(-1)) # => [3, 2]
@array.slice((4..-4).step(-2)) # => [4, 2]
@array.slice((4...-4).step(-2)) # => [3]
@array.slice((4..-4).step(-10)) # => [2]
@array.slice((4...-4).step(-10)) # => [2]
# start with negative index, end with negative index
@array.slice((-2..-4).step(-1)) # => [4, 3, 2]
@array.slice((-2...-4).step(-1)) # => [3, 2]
@array.slice((-2..-4).step(-2)) # => [4, 2]
@array.slice((-2...-4).step(-2)) # => [3]
@array.slice((-2..-4).step(-10)) # => [2]
@array.slice((-2...-4).step(-10)) # => [2]
```
Found while writing specs for this method in https://github.com/ruby/spec/pull/857