Note that ; $matrix[4][4]; only fills out the first level with five elements and populates the last with an array reference. This is because the last subscript doesn't do anything. Just like

if ($foo[100000] == 1) {
    ...
}
[download]

doesn't extend @foo to be 100001 elements. This is also why it gives a "useless use of array element in void context" warning.

The first level is extended though, but only filled with undefs except for the fifth element which becomes an array reference, which will be empty because of the reason above, looking like

[
    undef,
    undef,
    undef,
    undef,
    [ undef, undef, undef, undef , undef ],
]
[download]

Using the element in some way, not just using the value, like

$matrix[4][4] = undef
[download]

would fill out the array reference at index four in the first level, but the other levels would still be untouched, so you'd have a "half-expanded" 2D array, looking like

[
    undef,
    undef,
    undef,
    undef,
    [ undef, undef, undef, undef , undef ],
]
[download]

This is why Cody Pendant uses the for loop.

ihb

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