Bug #18688: when array's default value is empty hash adding a hash key value changes all array elements

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux]
• Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[pan (Pan Pan)]

ah = Array.new(3, {})
ah[1][:foo] = 'bar'
p ah # [{:foo=>"bar"}, {:foo=>"bar"}, {:foo=>"bar"}]

This is not expected result. The expected result is [{}, {:foo=>"bar"}, {}].
Alternatively, below code works as expected.

ah = Array.new(3) {{}}
ah[1][:foo] = 'bar'
p ah # [{}, {:foo=>"bar"}, {}]

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Rejected

This is expected behavior and not a bug. As you mentioned, you want to use the block form if you want a new object for each default value.