>perl -MDevel::Peek -e"$a[2]=undef; $a[3]=3; Dump \@a"
SV = RV(0x183c518) at 0x22609c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x226db0
  SV = PVAV(0x22bfcc) at 0x226db0
    REFCNT = 2
    FLAGS = ()
    IV = 0
    NV = 0
    ARRAY = 0x1833f9c
    FILL = 3
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0                        # Not allocated
    Elt No. 1                        # Not allocated
    Elt No. 2                        # Allocated but undef
    SV = NULL(0x0) at 0x225f7c
      REFCNT = 1
      FLAGS = ()
    Elt No. 3                        # Allocated and defined
    SV = IV(0x18287b4) at 0x22606c
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 3