From: Tim Pease <tim.pease@...>
Date: 2007-01-03T06:22:54+09:00
Subject: Re: Strange behaviour with array of arrays

On 1/2/07, Dan Stevens (IAmAI) <dan.stevens.iamai@gmail.com> wrote:
> Please observe the following code:
>
> # Create an array of arrays by explicitly stating values
> test1 = [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
> => [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
>
> # Create an array of arrays using new method
> test2 = Array.new(3, Array.new(3))
> => [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
>
> #Both arrays appear to be equal
> test1 == test2 => true
>
> # Modifying one of values behaves as expected
> test1[1][1] = true => true
> test1 => [[nil, nil, nil], [nil, true, nil], [nil, nil, nil]]
>
> # Modifying one of values behaves strangely
> test2[1][1] = true => true
> test2 => [[nil, true, nil], [nil, true, nil], [nil, true, nil]]
>
> Can anyone explain why this is happening as I don't understand why the
> two array should behave differently? This is assuming this isn't a
> bug.
>

The syntax you want is this ...

test2 = Array.new(3) {Array.new(3)}

This will create a new array of three elements and then create a a new
array object for each element of test2

test2 = Array.new(3, Array.new(3))

This will create a new array of three elements but use the same object
for element of test2

Blessings,
TwP