[ruby-core:105607] [Ruby master Bug#18247] weird results for `Array#slice` or `Array#[]` with argument of type `Enumerator::ArithmeticSequence`
From:
lxxxvi <noreply@...>
Date:
2021-10-08 15:38:39 UTC
List:
ruby-core #105607
Issue #18247 has been reported by lxxxvi (Mario Sch端ttel). ---------------------------------------- Bug #18247: weird results for `Array#slice` or `Array#[]` with argument of type `Enumerator::ArithmeticSequence` https://bugs.ruby-lang.org/issues/18247 * Author: lxxxvi (Mario Sch端ttel) * Status: Open * Priority: Normal * Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN ---------------------------------------- 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] ``` -- https://bugs.ruby-lang.org/ Unsubscribe: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>