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use Scalar::Util qw/dualvar/;
dualvar(0, '');

$ perl -wE 'say 1 + ""'
Argument "" isn't numeric in addition (+) at -e line 1.
1
$ perl -MScalar::Util=dualvar -wE 'say dualvar(0, "") + 1'
1

$ perl -MScalar::Util=dualvar -E 'my $x = dualvar(42, "23"); say $x; s
+ay $x + 1'
23
43

perl -MDevel::Peek -MScalar::Util=dualvar -e 'Dump !1; Dump dualvar(0,
+ "")'
SV = PVNV(0x254ff70) at 0x7409c0
...
  PV = 0x255f610 ""\0
  CUR = 0
  LEN = 8