Clone::PP provides a general-purpose clone function to make deep
 copies of Perl data structures. It calls itself recursively to copy
 nested hash, array, scalar and reference types, including tied
 variables and objects.
 .
 The clone() function takes a scalar argument to copy. To duplicate
 arrays or hashes, pass them in by reference:
 .
  my $copy = clone(\@array); my @copy = @{ clone(\@array) };
  my $copy = clone(\%hash); my %copy = %{ clone(\%hash) };
 .
 The clone() function also accepts an optional second parameter that
 can be used to limit the depth of the copy. If you pass a limit of
 0, clone will return the same value you supplied; for a limit of
 1, a shallow copy is constructed; for a limit of 2, two layers of
 copying are done, and so on.
 .
 This is a pure-perl implementation. For a faster XS-/C-based
 implementation see the libclone-perl package.