$ perl -MDP -wE'sub foo{DDumper[DDual($_[0])]};foo(42);foo("42");'
[   undef,
    42,
    undef,
    undef,
    0
    ]
[   42,
    undef,
    undef,
    undef,
    0
    ]
$ perl -MDP -wE'sub foo{DDual($_[0]);1;};foo(42);foo("42");'
IV(42)
  PV: SV_UNDEF
  IV: IV(42)
  NV: SV_UNDEF
  RV: SV_UNDEF
PV("42"\0)
  PV: PV("42"\0)
  IV: SV_UNDEF
  NV: SV_UNDEF
  RV: SV_UNDEF

##</code><code>##

my ($pv, $iv, $nv, $rv, $hm) = DDual ($var [, $getmagic])