@x{@y} = @z; means the same thing as:

foreach my $i (0 .. $#y)
{
    $x{$y[$i]} = $z[$i];
}
[download]

By extension, ++@x{@y}; means (roughly) the same thing as:

for my $i (0 .. $#y)
{
    $i == 0 ? $x{$y[$i]} = 1 : $x{$y[$i]} = undef;
}
[download]

Does that make sense now?

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.