Then , if you want to modify an existing data structure, what about using the fact that modifying $_ will modify the original array? Something like this, shown under the debugger:

  DB<1> @a = 1..9;

  DB<2>  map{ $_ = ++$_% 10 } @a;

  DB<3> x @a
0  2
1  3
2  4
3  5
4  6
5  7
6  8
7  9
8  0
  DB<4>
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Well, this obviously works, but something like $c = ++$c is, I believe, not defined in C and probably also not in Perl (i.e. the implementor if free to do whatever). It could be changed to:

map { $_ ++; $_ = $_ % 10} @a;
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This would probably be more secure against any change of implementation.