Bug #18741: Slicing an Array using index out of range inconsistent return type

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux-gnu]
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[leandrodesouzadev (Leandro de Souza)]

Hi there!
I've been learning ruby and following the Koans path. On the arrays part i get the following test case to handle:

  def test_slicing_arrays
    array = [:peanut, :butter, :and, :jelly]

    assert_equal [:peanut], array[0,1]
    assert_equal [:peanut, :butter], array[0,2]
    assert_equal [:and, :jelly], array[2,2]
    assert_equal [:and, :jelly], array[2,20]
    assert_equal [], array[4,0] # Out of range, returns empty array
    assert_equal [], array[4,100]
    assert_equal nil, array[5,0] # Also out of range, but returns nil
  end

It feels strange when an slice out of the range by one (1) returns an empty array, but when out of the range by two (2) returns nil.
I expected that the slice should either return nil/empty on both cases

[zverok (Victor Shepelev)]

I already raised the problem in #16822, it was closed by @matz (Yukihiro Matsumoto) with

I don't think the benefit of changing outweighs the pain of incompatibility. Rejected.

[ccmywish (Aoran Zeng)]

HI @zverok (Victor Shepelev), I think your proposition is a little different from what's reported here.

array = [:peanut, :butter, :and, :jelly]

# 4 is out of range, but -> []
array[4,0]

# 5 is out of range, but -> nil 
array[5,0]

Both out or range, why one [], one nil ?

[jeremyevans0 (Jeremy Evans)]

• Is duplicate of Feature #16822: Array slicing: nils and edge cases added

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Rejected