Bug #6580: Assigning a value to a single element in an array that is contained in an array of arrays, updates the element in that position in all of the contained arrays

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin10.8.0]

[jmoline (James Moline)]

=begin
Came across this bug the other day in both 1.8 and 1.9.3. It seems like it would have been discovered before, but I can't find anywhere that it has been reported.

Basically, when you have an array of arrays, and you attempt to assign a value to a single element of one of those arrays, it assigns the value to that element in all of the arrays.

Example:

(({arr = Array.new(5, Array.new(5))}))

[
[nil, nil, nil, nil, nil],
[nil, nil, nil, nil, nil],
[nil, nil, nil, nil, nil],
[nil, nil, nil, nil, nil],
[nil, nil, nil, nil, nil]
]

(({arr[0][0] = 3}))

[
[3, nil, nil, nil, nil],
[3, nil, nil, nil, nil],
[3, nil, nil, nil, nil],
[3, nil, nil, nil, nil],
[3, nil, nil, nil, nil],
]

(({arr[2][3] = "test"}))

[
[3, nil, nil, "test", nil],
[3, nil, nil, "test", nil],
[3, nil, nil, "test", nil],
[3, nil, nil, "test", nil],
[3, nil, nil, "test", nil],
]
=end

[jeremyevans0 (Jeremy Evans)]

This isn't a bug. You are creating an array where all five elements are the same array object. You probably want to do:

arr = Array.new(5){Array.new(5)}

That way each of the five elements in the outside array is a separate array.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Rejected