Bug #17058: Array#delete_if doesn't change array instantly

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[erik_schlyter (Erik Schlyter)]

According to the documentation: https://ruby-doc.org/core-2.7.1/Array.html#method-i-delete_if
"The array is changed instantly every time the block is called, not after the iteration is over."

I've tried printing the array while iterating it:

a = [1,2,3,4,5,6,7]
a.delete_if{|x|
  puts "During iteration: #{a}"
  x % 2 == 0
}
puts "After iteration: #{a}"

The output is as follows:

During iteration: [1, 2, 3, 4, 5, 6, 7]
During iteration: [1, 2, 3, 4, 5, 6, 7]
During iteration: [1, 2, 3, 4, 5, 6, 7]
During iteration: [1, 3, 3, 4, 5, 6, 7]
During iteration: [1, 3, 3, 4, 5, 6, 7]
During iteration: [1, 3, 5, 4, 5, 6, 7]
During iteration: [1, 3, 5, 4, 5, 6, 7]
After iteration: [1, 3, 5, 7]

This functionality has changed somewhere between 2.2.2 and 2.4.0. When I use "ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-linux]", I get the following (correct) output:

During iteration: [1, 2, 3, 4, 5, 6, 7]
During iteration: [1, 2, 3, 4, 5, 6, 7]
During iteration: [1, 3, 4, 5, 6, 7]
During iteration: [1, 3, 4, 5, 6, 7]
During iteration: [1, 3, 5, 6, 7]
During iteration: [1, 3, 5, 6, 7]
During iteration: [1, 3, 5, 7]
After iteration: [1, 3, 5, 7]

When I use "ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-linux]" or the latest (2.7.1), I get the wrong output.

The functionality doesn't seem crucial, but the documentation should be correct.

[jeremyevans0 (Jeremy Evans)]

Looks like this changed between Ruby 2.2 and 2.3. I'll update the documentation to remove the line, as I think it's an implementation detail (that is now wrong).

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

Actually, this was already fixed in 9fc25811d59422355fc3a0ed0f28155e4e47267f.