DB<126> use  Devel::Peek

  DB<127> sub tst_update { Dump(\@_); $_[0]=666; Dump(\@_) }

  DB<128> my $x=42; Dump($x); tst_update $x
SV = IV(0x88f2498) at 0x88f249c                    # <--- SV for $x
  REFCNT = 1
  FLAGS = (PADMY,IOK,pIOK)
  IV = 42
SV = IV(0x8d02430) at 0x8d02434
  REFCNT = 1
  FLAGS = (ROK)
  RV = 0x8a5cbbc
  SV = PVAV(0x89be074) at 0x8a5cbbc
    REFCNT = 3
    FLAGS = ()
    ARRAY = 0x86d4500
    FILL = 0
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x88f2498) at 0x88f249c                # <--- SV for $x
      REFCNT = 2
      FLAGS = (PADMY,IOK,pIOK)
      IV = 42
SV = IV(0x8d02430) at 0x8d02434
  REFCNT = 1
  FLAGS = (ROK)
  RV = 0x8a5cbbc
  SV = PVAV(0x89be074) at 0x8a5cbbc
    REFCNT = 3
    FLAGS = ()
    ARRAY = 0x86d4500
    FILL = 0
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x88f2498) at 0x88f249c                # <--- SV for $x
      REFCNT = 2
      FLAGS = (PADMY,IOK,pIOK)
      IV = 666