return doesn't change @_.

@_ is an array of aliases to the actual arguments, so changing @_ changes the actual arguments. 

sub { ++$_ for @_ }->(my @arr = 'a' .. 'c'); print "@arr";
# Output: b c d

[download]

In your case, it's bit more complex. Changing the function to 

sub reverseArray {
    my @arr = @_;
    for my $i (0 .. $#arr) {
        @{ $arr[$i] } = reverse @{ $arr[$i] };
    }
}

[download]
wouldn't have helped, as you're working with an array of arrays. The inner arrays are represented as references, so even if you store the references in a different @arr, they still refer to the same inner arrays.

To keep the array unchanged, only assign to the copy, don't change the references from the original array. 

sub reverseArray {
    my @arr = @_;
    for my $i (0 .. $#arr) {
        $arr[$i] = [ reverse @{ $arr[$i] } ];
    }
}

[download]
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Array value changing for some reason by choroba
in thread Array value changing for some reason by Silt

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