Ruby

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:

@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:

@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.

@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