$ perl -MDevel::Peek -e'@a=qw( a b c ); sub { Dump($_[0]) }->( $#a );'
SV = PVMG(0x1d36630) at 0x1cfcfd0
  REFCNT = 1
  FLAGS = (GMG,SMG)
  IV = 0
  NV = 0
  PV = 0
  MAGIC = 0x1cf6ab0
    MG_VIRTUAL = &PL_vtbl_arylen
    MG_TYPE = PERL_MAGIC_arylen(#)
    MG_OBJ = 0x1d07d10