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

##</code><code>##

$ 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

##</code><code>##

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

##</code><code>##

perl -MDevel::Peek -MScalar::Util=dualvar -e 'Dump !1; Dump dualvar(0, "")'
SV = PVNV(0x254ff70) at 0x7409c0
  REFCNT = 2147483647
  FLAGS = (IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x254ff50 ""\0
  CUR = 0
  LEN = 8
SV = PVNV(0x2550d90) at 0x2551220
  REFCNT = 1
  FLAGS = (TEMP,IOK,POK,pIOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x255f610 ""\0
  CUR = 0
  LEN = 8